Recovering From System Faults For Replicated Datasets

ABSTRACT

Recovering from system faults for replicated datasets, including: receiving, by the cloud-based storage system, a request to modify a dataset that is stored by the cloud-based storage system, wherein the dataset is synchronously replicated among a plurality of storage systems that includes the cloud-based storage system, wherein a request to modify the dataset is acknowledged as being complete when each of the plurality of storage systems has modified its copy of the dataset; generating recovery information indicating whether the request to modify the dataset has been applied on all storage systems in the plurality of storage systems synchronously replicating the dataset; and after a system fault, applying a recovery action in dependence upon the recovery information indicating whether the request to modify the dataset has been applied on all storage systems in the plurality of storage systems synchronously replicating the dataset.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application for patent entitled to a filing dateand claiming the benefit of earlier-filed U.S. Pat. No. 11,288,138,issued Mar. 29, 2022, herein incorporated by reference in its entirety.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates a first example system for data storage inaccordance with some implementations.

FIG. 1B illustrates a second example system for data storage inaccordance with some implementations.

FIG. 1C illustrates a third example system for data storage inaccordance with some implementations.

FIG. 1D illustrates a fourth example system for data storage inaccordance with some implementations.

FIG. 2A is a perspective view of a storage cluster with multiple storagenodes and internal storage coupled to each storage node to providenetwork attached storage, in accordance with some embodiments.

FIG. 2B is a block diagram showing an interconnect switch couplingmultiple storage nodes in accordance with some embodiments.

FIG. 2C is a multiple level block diagram, showing contents of a storagenode and contents of one of the non-volatile solid state storage unitsin accordance with some embodiments.

FIG. 2D shows a storage server environment, which uses embodiments ofthe storage nodes and storage units of some previous figures inaccordance with some embodiments.

FIG. 2E is a blade hardware block diagram, showing a control plane,compute and storage planes, and authorities interacting with underlyingphysical resources, in accordance with some embodiments.

FIG. 2F depicts elasticity software layers in blades of a storagecluster, in accordance with some embodiments.

FIG. 2G depicts authorities and storage resources in blades of a storagecluster, in accordance with some embodiments.

FIG. 3A sets forth a diagram of a storage system that is coupled fordata communications with a cloud services provider in accordance withsome embodiments of the present disclosure.

FIG. 3B sets forth a diagram of a storage system in accordance with someembodiments of the present disclosure.

FIG. 3C sets forth a diagram of a storage system in accordance with someembodiments of the present disclosure.

FIG. 3D sets forth a diagram of a storage system in accordance with someembodiments of the present disclosure.

FIG. 4 sets forth a block diagram illustrating a plurality of storagesystems that support a pod according to some embodiments of the presentdisclosure.

FIG. 5 sets forth a flow chart illustrating an example method ofestablishing a synchronous replication relationship between two or morestorage systems according to some embodiments of the present disclosure.

FIG. 6 sets forth a flow chart illustrating an example method ofestablishing a synchronous replication relationship between two or morestorage systems according to some embodiments of the present disclosure.

FIG. 7 sets forth a flow chart illustrating an example method ofestablishing a synchronous replication relationship between two or morestorage systems according to some embodiments of the present disclosure.

FIG. 8 sets forth a block diagram illustrating a plurality of storagesystems that support a pod according to some embodiments of the presentdisclosure.

FIG. 9 sets forth an example of a cloud-based storage system inaccordance with some embodiments of the present disclosure.

FIG. 10 sets forth a flow chart illustrating an example method ofservicing I/O operations in a cloud-based storage system.

FIG. 11 sets forth a flow chart illustrating an example method ofservicing I/O operations in a cloud-based storage system.

FIG. 12 sets forth a flow chart illustrating an example method ofservicing I/O operations in a cloud-based storage system.

FIG. 13 sets forth a flow chart illustrating an additional examplemethod of servicing I/O operations in a cloud-based storage system.

FIG. 14 sets forth a flow chart illustrating an example method forrecovery in a cloud-based storage system according to some embodimentsof the present disclosure.

DESCRIPTION OF EMBODIMENTS

Example methods, apparatus, and products for recovery in a cloud-basedstorage system in accordance with embodiments of the present disclosureare described with reference to the accompanying drawings, beginningwith FIG. 1A. FIG. 1A illustrates an example system for data storage, inaccordance with some implementations. System 100 (also referred to as“storage system” herein) includes numerous elements for purposes ofillustration rather than limitation. It may be noted that system 100 mayinclude the same, more, or fewer elements configured in the same ordifferent manner in other implementations.

System 100 includes a number of computing devices 164A-B. Computingdevices (also referred to as “client devices” herein) may be embodied,for example, a server in a data center, a workstation, a personalcomputer, a notebook, or the like. Computing devices 164A-B may becoupled for data communications to one or more storage arrays 102A-Bthrough a storage area network (‘SAN’) 158 or a local area network(‘LAN’) 160.

The SAN 158 may be implemented with a variety of data communicationsfabrics, devices, and protocols. For example, the fabrics for SAN 158may include Fibre Channel, Ethernet, InfiniBand, Serial Attached SmallComputer System Interface (‘SAS’), or the like. Data communicationsprotocols for use with SAN 158 may include Advanced TechnologyAttachment (‘ATA’), Fibre Channel Protocol, Small Computer SystemInterface (‘SCSI’), Internet Small Computer System Interface (‘iSCSI’),HyperSCSI, Non-Volatile Memory Express (‘NVMe’) over Fabrics, or thelike. It may be noted that SAN 158 is provided for illustration, ratherthan limitation. Other data communication couplings may be implementedbetween computing devices 164A-B and storage arrays 102A-B.

The LAN 160 may also be implemented with a variety of fabrics, devices,and protocols. For example, the fabrics for LAN 160 may include Ethernet(802.3), wireless (802.11), or the like. Data communication protocolsfor use in LAN 160 may include Transmission Control Protocol (‘TCP’),User Datagram Protocol (‘UDP’), Internet Protocol (‘IP’), HyperTextTransfer Protocol (‘HTTP’), Wireless Access Protocol (‘WAP’), HandheldDevice Transport Protocol (‘HDTP’), Session Initiation Protocol (‘SIP’),Real Time Protocol (‘RTP’), or the like.

Storage arrays 102A-B may provide persistent data storage for thecomputing devices 164A-B. Storage array 102A may be contained in achassis (not shown), and storage array 102B may be contained in anotherchassis (not shown), in implementations. Storage array 102A and 102B mayinclude one or more storage array controllers 110A-D (also referred toas “controller” herein). A storage array controller 110A-D may beembodied as a module of automated computing machinery comprisingcomputer hardware, computer software, or a combination of computerhardware and software. In some implementations, the storage arraycontrollers 110A-D may be configured to carry out various storage tasks.Storage tasks may include writing data received from the computingdevices 164A-B to storage array 102A-B, erasing data from storage array102A-B, retrieving data from storage array 102A-B and providing data tocomputing devices 164A-B, monitoring and reporting of disk utilizationand performance, performing redundancy operations, such as RedundantArray of Independent Drives (‘RAID’) or RAID-like data redundancyoperations, compressing data, encrypting data, and so forth.

Storage array controller 110A-D may be implemented in a variety of ways,including as a Field Programmable Gate Array (‘FPGA’), a ProgrammableLogic Chip (‘PLC’), an Application Specific Integrated Circuit (‘ASIC’),System-on-Chip (‘SOC’), or any computing device that includes discretecomponents such as a processing device, central processing unit,computer memory, or various adapters. Storage array controller 110A-Dmay include, for example, a data communications adapter configured tosupport communications via the SAN 158 or LAN 160. In someimplementations, storage array controller 110A-D may be independentlycoupled to the LAN 160. In implementations, storage array controller110A-D may include an I/O controller or the like that couples thestorage array controller 110A-D for data communications, through amidplane (not shown), to a persistent storage resource 170A-B (alsoreferred to as a “storage resource” herein). The persistent storageresource 170A-B main include any number of storage drives 171A-F (alsoreferred to as “storage devices” herein) and any number of non-volatileRandom Access Memory (‘NVRAM’) devices (not shown).

In some implementations, the NVRAM devices of a persistent storageresource 170A-B may be configured to receive, from the storage arraycontroller 110A-D, data to be stored in the storage drives 171A-F. Insome examples, the data may originate from computing devices 164A-B. Insome examples, writing data to the NVRAM device may be carried out morequickly than directly writing data to the storage drive 171A-F. Inimplementations, the storage array controller 110A-D may be configuredto utilize the NVRAM devices as a quickly accessible buffer for datadestined to be written to the storage drives 171A-F. Latency for writerequests using NVRAM devices as a buffer may be improved relative to asystem in which a storage array controller 110A-D writes data directlyto the storage drives 171A-F. In some implementations, the NVRAM devicesmay be implemented with computer memory in the form of high bandwidth,low latency RAM. The NVRAM device is referred to as “non-volatile”because the NVRAM device may receive or include a unique power sourcethat maintains the state of the RAM after main power loss to the NVRAMdevice. Such a power source may be a battery, one or more capacitors, orthe like. In response to a power loss, the NVRAM device may beconfigured to write the contents of the RAM to a persistent storage,such as the storage drives 171A-F.

In implementations, storage drive 171A-F may refer to any deviceconfigured to record data persistently, where “persistently” or“persistent” refers as to a device's ability to maintain recorded dataafter loss of power. In some implementations, storage drive 171A-F maycorrespond to non-disk storage media. For example, the storage drive171A-F may be one or more solid-state drives (‘SSDs’), flash memorybased storage, any type of solid-state non-volatile memory, or any othertype of non-mechanical storage device. In other implementations, storagedrive 171A-F may include mechanical or spinning hard disk, such ashard-disk drives (‘HDD’).

In some implementations, the storage array controllers 110A-D may beconfigured for offloading device management responsibilities fromstorage drive 171A-F in storage array 102A-B. For example, storage arraycontrollers 110A-D may manage control information that may describe thestate of one or more memory blocks in the storage drives 171A-F. Thecontrol information may indicate, for example, that a particular memoryblock has failed and should no longer be written to, that a particularmemory block contains boot code for a storage array controller 110A-D,the number of program-erase (‘P/E’) cycles that have been performed on aparticular memory block, the age of data stored in a particular memoryblock, the type of data that is stored in a particular memory block, andso forth. In some implementations, the control information may be storedwith an associated memory block as metadata. In other implementations,the control information for the storage drives 171A-F may be stored inone or more particular memory blocks of the storage drives 171A-F thatare selected by the storage array controller 110A-D. The selected memoryblocks may be tagged with an identifier indicating that the selectedmemory block contains control information. The identifier may beutilized by the storage array controllers 110A-D in conjunction withstorage drives 171A-F to quickly identify the memory blocks that containcontrol information. For example, the storage controllers 110A-D mayissue a command to locate memory blocks that contain controlinformation. It may be noted that control information may be so largethat parts of the control information may be stored in multiplelocations, that the control information may be stored in multiplelocations for purposes of redundancy, for example, or that the controlinformation may otherwise be distributed across multiple memory blocksin the storage drive 171A-F.

In implementations, storage array controllers 110A-D may offload devicemanagement responsibilities from storage drives 171A-F of storage array102A-B by retrieving, from the storage drives 171A-F, controlinformation describing the state of one or more memory blocks in thestorage drives 171A-F. Retrieving the control information from thestorage drives 171A-F may be carried out, for example, by the storagearray controller 110A-D querying the storage drives 171A-F for thelocation of control information for a particular storage drive 171A-F.The storage drives 171A-F may be configured to execute instructions thatenable the storage drive 171A-F to identify the location of the controlinformation. The instructions may be executed by a controller (notshown) associated with or otherwise located on the storage drive 171A-Fand may cause the storage drive 171A-F to scan a portion of each memoryblock to identify the memory blocks that store control information forthe storage drives 171A-F. The storage drives 171A-F may respond bysending a response message to the storage array controller 110A-D thatincludes the location of control information for the storage drive171A-F. Responsive to receiving the response message, storage arraycontrollers 110A-D may issue a request to read data stored at theaddress associated with the location of control information for thestorage drives 171A-F.

In other implementations, the storage array controllers 110A-D mayfurther offload device management responsibilities from storage drives171A-F by performing, in response to receiving the control information,a storage drive management operation. A storage drive managementoperation may include, for example, an operation that is typicallyperformed by the storage drive 171A-F (e.g., the controller (not shown)associated with a particular storage drive 171A-F). A storage drivemanagement operation may include, for example, ensuring that data is notwritten to failed memory blocks within the storage drive 171A-F,ensuring that data is written to memory blocks within the storage drive171A-F in such a way that adequate wear leveling is achieved, and soforth.

In implementations, storage array 102A-B may implement two or morestorage array controllers 110A-D. For example, storage array 102A mayinclude storage array controllers 110A and storage array controllers110B. At a given instance, a single storage array controller 110A-D(e.g., storage array controller 110A) of a storage system 100 may bedesignated with primary status (also referred to as “primary controller”herein), and other storage array controllers 110A-D (e.g., storage arraycontroller 110A) may be designated with secondary status (also referredto as “secondary controller” herein). The primary controller may haveparticular rights, such as permission to alter data in persistentstorage resource 170A-B (e.g., writing data to persistent storageresource 170A-B). At least some of the rights of the primary controllermay supersede the rights of the secondary controller. For instance, thesecondary controller may not have permission to alter data in persistentstorage resource 170A-B when the primary controller has the right. Thestatus of storage array controllers 110A-D may change. For example,storage array controller 110A may be designated with secondary status,and storage array controller 110B may be designated with primary status.

In some implementations, a primary controller, such as storage arraycontroller 110A, may serve as the primary controller for one or morestorage arrays 102A-B, and a second controller, such as storage arraycontroller 110B, may serve as the secondary controller for the one ormore storage arrays 102A-B. For example, storage array controller 110Amay be the primary controller for storage array 102A and storage array102B, and storage array controller 110B may be the secondary controllerfor storage array 102A and 102B. In some implementations, storage arraycontrollers 110C and 110D (also referred to as “storage processingmodules”) may neither have primary or secondary status. Storage arraycontrollers 110C and 110D, implemented as storage processing modules,may act as a communication interface between the primary and secondarycontrollers (e.g., storage array controllers 110A and 110B,respectively) and storage array 102B. For example, storage arraycontroller 110A of storage array 102A may send a write request, via SAN158, to storage array 102B. The write request may be received by bothstorage array controllers 110C and 110D of storage array 102B. Storagearray controllers 110C and 110D facilitate the communication, e.g., sendthe write request to the appropriate storage drive 171A-F. It may benoted that in some implementations storage processing modules may beused to increase the number of storage drives controlled by the primaryand secondary controllers.

In implementations, storage array controllers 110A-D are communicativelycoupled, via a midplane (not shown), to one or more storage drives171A-F and to one or more NVRAM devices (not shown) that are included aspart of a storage array 102A-B. The storage array controllers 110A-D maybe coupled to the midplane via one or more data communication links andthe midplane may be coupled to the storage drives 171A-F and the NVRAMdevices via one or more data communications links. The datacommunications links described herein are collectively illustrated bydata communications links 108A-D and may include a Peripheral ComponentInterconnect Express (‘PCIe’) bus, for example.

FIG. 1B illustrates an example system for data storage, in accordancewith some implementations. Storage array controller 101 illustrated inFIG. 1B may be similar to the storage array controllers 110A-D describedwith respect to FIG. 1A. In one example, storage array controller 101may be similar to storage array controller 110A or storage arraycontroller 110B. Storage array controller 101 includes numerous elementsfor purposes of illustration rather than limitation. It may be notedthat storage array controller 101 may include the same, more, or fewerelements configured in the same or different manner in otherimplementations. It may be noted that elements of FIG. 1A may beincluded below to help illustrate features of storage array controller101.

Storage array controller 101 may include one or more processing devices104 and random access memory (‘RAM’) 111. Processing device 104 (orcontroller 101) represents one or more general-purpose processingdevices such as a microprocessor, central processing unit, or the like.More particularly, the processing device 104 (or controller 101) may bea complex instruction set computing (‘CISC’) microprocessor, reducedinstruction set computing (‘RISC’) microprocessor, very long instructionword (‘VLIW’) microprocessor, or a processor implementing otherinstruction sets or processors implementing a combination of instructionsets. The processing device 104 (or controller 101) may also be one ormore special-purpose processing devices such as an application specificintegrated circuit (‘ASIC’), a field programmable gate array (‘FPGA’), adigital signal processor (‘DSP’), network processor, or the like.

The processing device 104 may be connected to the RAM 111 via a datacommunications link 106, which may be embodied as a high speed memorybus such as a Double-Data Rate 4 (‘DDR4’) bus. Stored in RAM 111 is anoperating system 112. In some implementations, instructions 113 arestored in RAM 111. Instructions 113 may include computer programinstructions for performing operations in a direct-mapped flash storagesystem. In one embodiment, a direct-mapped flash storage system is onethat that addresses data blocks within flash drives directly and withoutan address translation performed by the storage controllers of the flashdrives.

In implementations, storage array controller 101 includes one or morehost bus adapters 103A-C that are coupled to the processing device 104via a data communications link 105A-C. In implementations, host busadapters 103A-C may be computer hardware that connects a host system(e.g., the storage array controller) to other network and storagearrays. In some examples, host bus adapters 103A-C may be a FibreChannel adapter that enables the storage array controller 101 to connectto a SAN, an Ethernet adapter that enables the storage array controller101 to connect to a LAN, or the like. Host bus adapters 103A-C may becoupled to the processing device 104 via a data communications link105A-C such as, for example, a PCIe bus.

In implementations, storage array controller 101 may include a host busadapter 114 that is coupled to an expander 115. The expander 115 may beused to attach a host system to a larger number of storage drives. Theexpander 115 may, for example, be a SAS expander utilized to enable thehost bus adapter 114 to attach to storage drives in an implementationwhere the host bus adapter 114 is embodied as a SAS controller.

In implementations, storage array controller 101 may include a switch116 coupled to the processing device 104 via a data communications link109. The switch 116 may be a computer hardware device that can createmultiple endpoints out of a single endpoint, thereby enabling multipledevices to share a single endpoint. The switch 116 may, for example, bea PCIe switch that is coupled to a PCIe bus (e.g., data communicationslink 109) and presents multiple PCIe connection points to the midplane.

In implementations, storage array controller 101 includes a datacommunications link 107 for coupling the storage array controller 101 toother storage array controllers. In some examples, data communicationslink 107 may be a QuickPath Interconnect (QPI) interconnect.

A traditional storage system that uses traditional flash drives mayimplement a process across the flash drives that are part of thetraditional storage system. For example, a higher level process of thestorage system may initiate and control a process across the flashdrives. However, a flash drive of the traditional storage system mayinclude its own storage controller that also performs the process. Thus,for the traditional storage system, a higher level process (e.g.,initiated by the storage system) and a lower level process (e.g.,initiated by a storage controller of the storage system) may both beperformed.

To resolve various deficiencies of a traditional storage system,operations may be performed by higher level processes and not by thelower level processes. For example, the flash storage system may includeflash drives that do not include storage controllers that provide theprocess. Thus, the operating system of the flash storage system itselfmay initiate and control the process. This may be accomplished by adirect-mapped flash storage system that addresses data blocks within theflash drives directly and without an address translation performed bythe storage controllers of the flash drives.

The operating system of the flash storage system may identify andmaintain a list of allocation units across multiple flash drives of theflash storage system. The allocation units may be entire erase blocks ormultiple erase blocks. The operating system may maintain a map oraddress range that directly maps addresses to erase blocks of the flashdrives of the flash storage system.

Direct mapping to the erase blocks of the flash drives may be used torewrite data and erase data. For example, the operations may beperformed on one or more allocation units that include a first data anda second data where the first data is to be retained and the second datais no longer being used by the flash storage system. The operatingsystem may initiate the process to write the first data to new locationswithin other allocation units and erasing the second data and markingthe allocation units as being available for use for subsequent data.Thus, the process may only be performed by the higher level operatingsystem of the flash storage system without an additional lower levelprocess being performed by controllers of the flash drives.

Advantages of the process being performed only by the operating systemof the flash storage system include increased reliability of the flashdrives of the flash storage system as unnecessary or redundant writeoperations are not being performed during the process. One possiblepoint of novelty here is the concept of initiating and controlling theprocess at the operating system of the flash storage system. Inaddition, the process can be controlled by the operating system acrossmultiple flash drives. This is contrast to the process being performedby a storage controller of a flash drive.

A storage system can consist of two storage array controllers that sharea set of drives for failover purposes, or it could consist of a singlestorage array controller that provides a storage service that utilizesmultiple drives, or it could consist of a distributed network of storagearray controllers each with some number of drives or some amount ofFlash storage where the storage array controllers in the networkcollaborate to provide a complete storage service and collaborate onvarious aspects of a storage service including storage allocation andgarbage collection.

FIG. 1C illustrates a third example system 117 for data storage inaccordance with some implementations. System 117 (also referred to as“storage system” herein) includes numerous elements for purposes ofillustration rather than limitation. It may be noted that system 117 mayinclude the same, more, or fewer elements configured in the same ordifferent manner in other implementations.

In one embodiment, system 117 includes a dual Peripheral ComponentInterconnect (‘PCI’) flash storage device 118 with separatelyaddressable fast write storage. System 117 may include a storagecontroller 119. In one embodiment, storage controller 119A-D may be aCPU, ASIC, FPGA, or any other circuitry that may implement controlstructures necessary according to the present disclosure. In oneembodiment, system 117 includes flash memory devices (e.g., includingflash memory devices 120 a-n), operatively coupled to various channelsof the storage device controller 119. Flash memory devices 120 a-n, maybe presented to the controller 119A-D as an addressable collection ofFlash pages, erase blocks, and/or control elements sufficient to allowthe storage device controller 119A-D to program and retrieve variousaspects of the Flash. In one embodiment, storage device controller119A-D may perform operations on flash memory devices 120 a-n includingstoring and retrieving data content of pages, arranging and erasing anyblocks, tracking statistics related to the use and reuse of Flash memorypages, erase blocks, and cells, tracking and predicting error codes andfaults within the Flash memory, controlling voltage levels associatedwith programming and retrieving contents of Flash cells, etc.

In one embodiment, system 117 may include RAM 121 to store separatelyaddressable fast-write data. In one embodiment, RAM 121 may be one ormore separate discrete devices. In another embodiment, RAM 121 may beintegrated into storage device controller 119A-D or multiple storagedevice controllers. The RAM 121 may be utilized for other purposes aswell, such as temporary program memory for a processing device (e.g., aCPU) in the storage device controller 119.

In one embodiment, system 117 may include a stored energy device 122,such as a rechargeable battery or a capacitor. Stored energy device 122may store energy sufficient to power the storage device controller 119,some amount of the RAM (e.g., RAM 121), and some amount of Flash memory(e.g., Flash memory 120 a-120 n) for sufficient time to write thecontents of RAM to Flash memory. In one embodiment, storage devicecontroller 119A-D may write the contents of RAM to Flash Memory if thestorage device controller detects loss of external power.

In one embodiment, system 117 includes two data communications links 123a, 123 b. In one embodiment, data communications links 123 a, 123 b maybe PCI interfaces. In another embodiment, data communications links 123a, 123 b may be based on other communications standards (e.g.,HyperTransport, InfiniBand, etc.). Data communications links 123 a, 123b may be based on non-volatile memory express (‘NVMe’) or NVMe overfabrics (‘NVMf’) specifications that allow external connection to thestorage device controller 119A-D from other components in the storagesystem 117. It should be noted that data communications links may beinterchangeably referred to herein as PCI buses for convenience.

System 117 may also include an external power source (not shown), whichmay be provided over one or both data communications links 123 a, 123 b,or which may be provided separately. An alternative embodiment includesa separate Flash memory (not shown) dedicated for use in storing thecontent of RAM 121. The storage device controller 119A-D may present alogical device over a PCI bus which may include an addressablefast-write logical device, or a distinct part of the logical addressspace of the storage device 118, which may be presented as PCI memory oras persistent storage. In one embodiment, operations to store into thedevice are directed into the RAM 121. On power failure, the storagedevice controller 119A-D may write stored content associated with theaddressable fast-write logical storage to Flash memory (e.g., Flashmemory 120 a-n) for long-term persistent storage.

In one embodiment, the logical device may include some presentation ofsome or all of the content of the Flash memory devices 120 a-n, wherethat presentation allows a storage system including a storage device 118(e.g., storage system 117) to directly address Flash memory pages anddirectly reprogram erase blocks from storage system components that areexternal to the storage device through the PCI bus. The presentation mayalso allow one or more of the external components to control andretrieve other aspects of the Flash memory including some or all of:tracking statistics related to use and reuse of Flash memory pages,erase blocks, and cells across all the Flash memory devices; trackingand predicting error codes and faults within and across the Flash memorydevices; controlling voltage levels associated with programming andretrieving contents of Flash cells; etc.

In one embodiment, the stored energy device 122 may be sufficient toensure completion of in-progress operations to the Flash memory devices120 a-120 n stored energy device 122 may power storage device controller119A-D and associated Flash memory devices (e.g., 120 a-n) for thoseoperations, as well as for the storing of fast-write RAM to Flashmemory. Stored energy device 122 may be used to store accumulatedstatistics and other parameters kept and tracked by the Flash memorydevices 120 a-n and/or the storage device controller 119. Separatecapacitors or stored energy devices (such as smaller capacitors near orembedded within the Flash memory devices themselves) may be used forsome or all of the operations described herein.

Various schemes may be used to track and optimize the life span of thestored energy component, such as adjusting voltage levels over time,partially discharging the storage energy device 122 to measurecorresponding discharge characteristics, etc. If the available energydecreases over time, the effective available capacity of the addressablefast-write storage may be decreased to ensure that it can be writtensafely based on the currently available stored energy.

FIG. 1D illustrates a third example system 124 for data storage inaccordance with some implementations. In one embodiment, system 124includes storage controllers 125 a, 125 b. In one embodiment, storagecontrollers 125 a, 125 b are operatively coupled to Dual PCI storagedevices 119 a, 119 b and 119 c, 119 d, respectively. Storage controllers125 a, 125 b may be operatively coupled (e.g., via a storage network130) to some number of host computers 127 a-n.

In one embodiment, two storage controllers (e.g., 125 a and 125 b)provide storage services, such as a SCS) block storage array, a fileserver, an object server, a database or data analytics service, etc. Thestorage controllers 125 a, 125 b may provide services through somenumber of network interfaces (e.g., 126 a-d) to host computers 127 a-noutside of the storage system 124. Storage controllers 125 a, 125 b mayprovide integrated services or an application entirely within thestorage system 124, forming a converged storage and compute system. Thestorage controllers 125 a, 125 b may utilize the fast write memorywithin or across storage devices 119 a-d to journal in progressoperations to ensure the operations are not lost on a power failure,storage controller removal, storage controller or storage systemshutdown, or some fault of one or more software or hardware componentswithin the storage system 124.

In one embodiment, controllers 125 a, 125 b operate as PCI masters toone or the other PCI buses 128 a, 128 b. In another embodiment, 128 aand 128 b may be based on other communications standards (e.g.,HyperTransport, InfiniBand, etc.). Other storage system embodiments mayoperate storage controllers 125 a, 125 b as multi-masters for both PCIbuses 128 a, 128 b. Alternately, a PCI/NVMe/NVMf switchinginfrastructure or fabric may connect multiple storage controllers. Somestorage system embodiments may allow storage devices to communicate witheach other directly rather than communicating only with storagecontrollers. In one embodiment, a storage device controller 119 a may beoperable under direction from a storage controller 125 a to synthesizeand transfer data to be stored into Flash memory devices from data thathas been stored in RAM (e.g., RAM 121 of FIG. 1C). For example, arecalculated version of RAM content may be transferred after a storagecontroller has determined that an operation has fully committed acrossthe storage system, or when fast-write memory on the device has reacheda certain used capacity, or after a certain amount of time, to ensureimprove safety of the data or to release addressable fast-write capacityfor reuse. This mechanism may be used, for example, to avoid a secondtransfer over a bus (e.g., 128 a, 128 b) from the storage controllers125 a, 125 b. In one embodiment, a recalculation may include compressingdata, attaching indexing or other metadata, combining multiple datasegments together, performing erasure code calculations, etc.

In one embodiment, under direction from a storage controller 125 a, 125b, a storage device controller 119 a, 119 b may be operable to calculateand transfer data to other storage devices from data stored in RAM(e.g., RAM 121 of FIG. 1C) without involvement of the storagecontrollers 125 a, 125 b. This operation may be used to mirror datastored in one controller 125 a to another controller 125 b, or it couldbe used to offload compression, data aggregation, and/or erasure codingcalculations and transfers to storage devices to reduce load on storagecontrollers or the storage controller interface 129 a, 129 b to the PCIbus 128 a, 128 b.

A storage device controller 119A-D may include mechanisms forimplementing high availability primitives for use by other parts of astorage system external to the Dual PCI storage device 118. For example,reservation or exclusion primitives may be provided so that, in astorage system with two storage controllers providing a highly availablestorage service, one storage controller may prevent the other storagecontroller from accessing or continuing to access the storage device.This could be used, for example, in cases where one controller detectsthat the other controller is not functioning properly or where theinterconnect between the two storage controllers may itself not befunctioning properly.

In one embodiment, a storage system for use with Dual PCI direct mappedstorage devices with separately addressable fast write storage includessystems that manage erase blocks or groups of erase blocks as allocationunits for storing data on behalf of the storage service, or for storingmetadata (e.g., indexes, logs, etc.) associated with the storageservice, or for proper management of the storage system itself. Flashpages, which may be a few kilobytes in size, may be written as dataarrives or as the storage system is to persist data for long intervalsof time (e.g., above a defined threshold of time). To commit data morequickly, or to reduce the number of writes to the Flash memory devices,the storage controllers may first write data into the separatelyaddressable fast write storage on one more storage devices.

In one embodiment, the storage controllers 125 a, 125 b may initiate theuse of erase blocks within and across storage devices (e.g., 118) inaccordance with an age and expected remaining lifespan of the storagedevices, or based on other statistics. The storage controllers 125 a,125 b may initiate garbage collection and data migration data betweenstorage devices in accordance with pages that are no longer needed aswell as to manage Flash page and erase block lifespans and to manageoverall system performance.

In one embodiment, the storage system 124 may utilize mirroring and/orerasure coding schemes as part of storing data into addressable fastwrite storage and/or as part of writing data into allocation unitsassociated with erase blocks. Erasure codes may be used across storagedevices, as well as within erase blocks or allocation units, or withinand across Flash memory devices on a single storage device, to provideredundancy against single or multiple storage device failures or toprotect against internal corruptions of Flash memory pages resultingfrom Flash memory operations or from degradation of Flash memory cells.Mirroring and erasure coding at various levels may be used to recoverfrom multiple types of failures that occur separately or in combination.

The embodiments depicted with reference to FIGS. 2A-G illustrate astorage cluster that stores user data, such as user data originatingfrom one or more user or client systems or other sources external to thestorage cluster. The storage cluster distributes user data acrossstorage nodes housed within a chassis, or across multiple chassis, usingerasure coding and redundant copies of metadata. Erasure coding refersto a method of data protection or reconstruction in which data is storedacross a set of different locations, such as disks, storage nodes orgeographic locations. Flash memory is one type of solid-state memorythat may be integrated with the embodiments, although the embodimentsmay be extended to other types of solid-state memory or other storagemedium, including non-solid state memory. Control of storage locationsand workloads are distributed across the storage locations in aclustered peer-to-peer system. Tasks such as mediating communicationsbetween the various storage nodes, detecting when a storage node hasbecome unavailable, and balancing I/Os (inputs and outputs) across thevarious storage nodes, are all handled on a distributed basis. Data islaid out or distributed across multiple storage nodes in data fragmentsor stripes that support data recovery in some embodiments. Ownership ofdata can be reassigned within a cluster, independent of input and outputpatterns. This architecture described in more detail below allows astorage node in the cluster to fail, with the system remainingoperational, since the data can be reconstructed from other storagenodes and thus remain available for input and output operations. Invarious embodiments, a storage node may be referred to as a clusternode, a blade, or a server.

The storage cluster may be contained within a chassis, i.e., anenclosure housing one or more storage nodes. A mechanism to providepower to each storage node, such as a power distribution bus, and acommunication mechanism, such as a communication bus that enablescommunication between the storage nodes are included within the chassis.The storage cluster can run as an independent system in one locationaccording to some embodiments. In one embodiment, a chassis contains atleast two instances of both the power distribution and the communicationbus which may be enabled or disabled independently. The internalcommunication bus may be an Ethernet bus, however, other technologiessuch as PCIe, InfiniBand, and others, are equally suitable. The chassisprovides a port for an external communication bus for enablingcommunication between multiple chassis, directly or through a switch,and with client systems. The external communication may use a technologysuch as Ethernet, InfiniBand, Fibre Channel, etc. In some embodiments,the external communication bus uses different communication bustechnologies for inter-chassis and client communication. If a switch isdeployed within or between chassis, the switch may act as a translationbetween multiple protocols or technologies. When multiple chassis areconnected to define a storage cluster, the storage cluster may beaccessed by a client using either proprietary interfaces or standardinterfaces such as network file system (‘NFS’), common internet filesystem (‘CIFS’), small computer system interface (‘SCSI’) or hypertexttransfer protocol (‘HTTP’). Translation from the client protocol mayoccur at the switch, chassis external communication bus or within eachstorage node. In some embodiments, multiple chassis may be coupled orconnected to each other through an aggregator switch. A portion and/orall of the coupled or connected chassis may be designated as a storagecluster. As discussed above, each chassis can have multiple blades, eachblade has a media access control (‘MAC’) address, but the storagecluster is presented to an external network as having a single clusterIP address and a single MAC address in some embodiments.

Each storage node may be one or more storage servers and each storageserver is connected to one or more non-volatile solid state memoryunits, which may be referred to as storage units or storage devices. Oneembodiment includes a single storage server in each storage node andbetween one to eight non-volatile solid state memory units, however thisone example is not meant to be limiting. The storage server may includea processor, DRAM and interfaces for the internal communication bus andpower distribution for each of the power buses. Inside the storage node,the interfaces and storage unit share a communication bus, e.g., PCIExpress, in some embodiments. The non-volatile solid state memory unitsmay directly access the internal communication bus interface through astorage node communication bus, or request the storage node to accessthe bus interface. The non-volatile solid state memory unit contains anembedded CPU, solid state storage controller, and a quantity of solidstate mass storage, e.g., between 2-32 terabytes (‘TB’) in someembodiments. An embedded volatile storage medium, such as DRAM, and anenergy reserve apparatus are included in the non-volatile solid statememory unit. In some embodiments, the energy reserve apparatus is acapacitor, super-capacitor, or battery that enables transferring asubset of DRAM contents to a stable storage medium in the case of powerloss. In some embodiments, the non-volatile solid state memory unit isconstructed with a storage class memory, such as phase change ormagnetoresistive random access memory (‘MRAM’) that substitutes for DRAMand enables a reduced power hold-up apparatus.

One of many features of the storage nodes and non-volatile solid statestorage is the ability to proactively rebuild data in a storage cluster.The storage nodes and non-volatile solid state storage can determinewhen a storage node or non-volatile solid state storage in the storagecluster is unreachable, independent of whether there is an attempt toread data involving that storage node or non-volatile solid statestorage. The storage nodes and non-volatile solid state storage thencooperate to recover and rebuild the data in at least partially newlocations. This constitutes a proactive rebuild, in that the systemrebuilds data without waiting until the data is needed for a read accessinitiated from a client system employing the storage cluster. These andfurther details of the storage memory and operation thereof arediscussed below.

FIG. 2A is a perspective view of a storage cluster 161, with multiplestorage nodes 150 and internal solid-state memory coupled to eachstorage node to provide network attached storage or storage areanetwork, in accordance with some embodiments. A network attachedstorage, storage area network, or a storage cluster, or other storagememory, could include one or more storage clusters 161, each having oneor more storage nodes 150, in a flexible and reconfigurable arrangementof both the physical components and the amount of storage memoryprovided thereby. The storage cluster 161 is designed to fit in a rack,and one or more racks can be set up and populated as desired for thestorage memory. The storage cluster 161 has a chassis 138 havingmultiple slots 142. It should be appreciated that chassis 138 may bereferred to as a housing, enclosure, or rack unit. In one embodiment,the chassis 138 has fourteen slots 142, although other numbers of slotsare readily devised. For example, some embodiments have four slots,eight slots, sixteen slots, thirty-two slots, or other suitable numberof slots. Each slot 142 can accommodate one storage node 150 in someembodiments. Chassis 138 includes flaps 148 that can be utilized tomount the chassis 138 on a rack. Fans 144 provide air circulation forcooling of the storage nodes 150 and components thereof, although othercooling components could be used, or an embodiment could be devisedwithout cooling components. A switch fabric 146 couples storage nodes150 within chassis 138 together and to a network for communication tothe memory. In an embodiment depicted in herein, the slots 142 to theleft of the switch fabric 146 and fans 144 are shown occupied by storagenodes 150, while the slots 142 to the right of the switch fabric 146 andfans 144 are empty and available for insertion of storage node 150 forillustrative purposes. This configuration is one example, and one ormore storage nodes 150 could occupy the slots 142 in various furtherarrangements. The storage node arrangements need not be sequential oradjacent in some embodiments. Storage nodes 150 are hot pluggable,meaning that a storage node 150 can be inserted into a slot 142 in thechassis 138, or removed from a slot 142, without stopping or poweringdown the system. Upon insertion or removal of storage node 150 from slot142, the system automatically reconfigures in order to recognize andadapt to the change. Reconfiguration, in some embodiments, includesrestoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodimentshown here, the storage node 150 includes a printed circuit board 159populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU156, and a non-volatile solid state storage 152 coupled to the CPU 156,although other mountings and/or components could be used in furtherembodiments. The memory 154 has instructions which are executed by theCPU 156 and/or data operated on by the CPU 156. As further explainedbelow, the non-volatile solid state storage 152 includes flash or, infurther embodiments, other types of solid-state memory.

Referring to FIG. 2A, storage cluster 161 is scalable, meaning thatstorage capacity with non-uniform storage sizes is readily added, asdescribed above. One or more storage nodes 150 can be plugged into orremoved from each chassis and the storage cluster self-configures insome embodiments. Plug-in storage nodes 150, whether installed in achassis as delivered or later added, can have different sizes. Forexample, in one embodiment a storage node 150 can have any multiple of 4TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, astorage node 150 could have any multiple of other storage amounts orcapacities. Storage capacity of each storage node 150 is broadcast, andinfluences decisions of how to stripe the data. For maximum storageefficiency, an embodiment can self-configure as wide as possible in thestripe, subject to a predetermined requirement of continued operationwith loss of up to one, or up to two, non-volatile solid state storageunits 152 or storage nodes 150 within the chassis.

FIG. 2B is a block diagram showing a communications interconnect 173 andpower distribution bus 172 coupling multiple storage nodes 150.Referring back to FIG. 2A, the communications interconnect 173 can beincluded in or implemented with the switch fabric 146 in someembodiments. Where multiple storage clusters 161 occupy a rack, thecommunications interconnect 173 can be included in or implemented with atop of rack switch, in some embodiments. As illustrated in FIG. 2B,storage cluster 161 is enclosed within a single chassis 138. Externalport 176 is coupled to storage nodes 150 through communicationsinterconnect 173, while external port 174 is coupled directly to astorage node. External power port 178 is coupled to power distributionbus 172. Storage nodes 150 may include varying amounts and differingcapacities of non-volatile solid state storage 152 as described withreference to FIG. 2A. In addition, one or more storage nodes 150 may bea compute only storage node as illustrated in FIG. 2B. Authorities 168are implemented on the non-volatile solid state storages 152, forexample as lists or other data structures stored in memory. In someembodiments the authorities are stored within the non-volatile solidstate storage 152 and supported by software executing on a controller orother processor of the non-volatile solid state storage 152. In afurther embodiment, authorities 168 are implemented on the storage nodes150, for example as lists or other data structures stored in the memory154 and supported by software executing on the CPU 156 of the storagenode 150. Authorities 168 control how and where data is stored in thenon-volatile solid state storages 152 in some embodiments. This controlassists in determining which type of erasure coding scheme is applied tothe data, and which storage nodes 150 have which portions of the data.Each authority 168 may be assigned to a non-volatile solid state storage152. Each authority may control a range of inode numbers, segmentnumbers, or other data identifiers which are assigned to data by a filesystem, by the storage nodes 150, or by the non-volatile solid statestorage 152, in various embodiments.

Every piece of data, and every piece of metadata, has redundancy in thesystem in some embodiments. In addition, every piece of data and everypiece of metadata has an owner, which may be referred to as anauthority. If that authority is unreachable, for example through failureof a storage node, there is a plan of succession for how to find thatdata or that metadata. In various embodiments, there are redundantcopies of authorities 168. Authorities 168 have a relationship tostorage nodes 150 and non-volatile solid state storage 152 in someembodiments. Each authority 168, covering a range of data segmentnumbers or other identifiers of the data, may be assigned to a specificnon-volatile solid state storage 152. In some embodiments theauthorities 168 for all of such ranges are distributed over thenon-volatile solid state storages 152 of a storage cluster. Each storagenode 150 has a network port that provides access to the non-volatilesolid state storage(s) 152 of that storage node 150. Data can be storedin a segment, which is associated with a segment number and that segmentnumber is an indirection for a configuration of a RAID (redundant arrayof independent disks) stripe in some embodiments. The assignment and useof the authorities 168 thus establishes an indirection to data.Indirection may be referred to as the ability to reference dataindirectly, in this case via an authority 168, in accordance with someembodiments. A segment identifies a set of non-volatile solid statestorage 152 and a local identifier into the set of non-volatile solidstate storage 152 that may contain data. In some embodiments, the localidentifier is an offset into the device and may be reused sequentiallyby multiple segments. In other embodiments the local identifier isunique for a specific segment and never reused. The offsets in thenon-volatile solid state storage 152 are applied to locating data forwriting to or reading from the non-volatile solid state storage 152 (inthe form of a RAID stripe). Data is striped across multiple units ofnon-volatile solid state storage 152, which may include or be differentfrom the non-volatile solid state storage 152 having the authority 168for a particular data segment.

If there is a change in where a particular segment of data is located,e.g., during a data move or a data reconstruction, the authority 168 forthat data segment should be consulted, at that non-volatile solid statestorage 152 or storage node 150 having that authority 168. In order tolocate a particular piece of data, embodiments calculate a hash valuefor a data segment or apply an inode number or a data segment number.The output of this operation points to a non-volatile solid statestorage 152 having the authority 168 for that particular piece of data.In some embodiments there are two stages to this operation. The firststage maps an entity identifier (ID), e.g., a segment number, inodenumber, or directory number to an authority identifier. This mapping mayinclude a calculation such as a hash or a bit mask. The second stage ismapping the authority identifier to a particular non-volatile solidstate storage 152, which may be done through an explicit mapping. Theoperation is repeatable, so that when the calculation is performed, theresult of the calculation repeatably and reliably points to a particularnon-volatile solid state storage 152 having that authority 168. Theoperation may include the set of reachable storage nodes as input. Ifthe set of reachable non-volatile solid state storage units changes theoptimal set changes. In some embodiments, the persisted value is thecurrent assignment (which is always true) and the calculated value isthe target assignment the cluster will attempt to reconfigure towards.This calculation may be used to determine the optimal non-volatile solidstate storage 152 for an authority in the presence of a set ofnon-volatile solid state storage 152 that are reachable and constitutethe same cluster. The calculation also determines an ordered set of peernon-volatile solid state storage 152 that will also record the authorityto non-volatile solid state storage mapping so that the authority may bedetermined even if the assigned non-volatile solid state storage isunreachable. A duplicate or substitute authority 168 may be consulted ifa specific authority 168 is unavailable in some embodiments.

With reference to FIGS. 2A and 2B, two of the many tasks of the CPU 156on a storage node 150 are to break up write data, and reassemble readdata. When the system has determined that data is to be written, theauthority 168 for that data is located as above. When the segment ID fordata is already determined the request to write is forwarded to thenon-volatile solid state storage 152 currently determined to be the hostof the authority 168 determined from the segment. The host CPU 156 ofthe storage node 150, on which the non-volatile solid state storage 152and corresponding authority 168 reside, then breaks up or shards thedata and transmits the data out to various non-volatile solid statestorage 152. The transmitted data is written as a data stripe inaccordance with an erasure coding scheme. In some embodiments, data isrequested to be pulled, and in other embodiments, data is pushed. Inreverse, when data is read, the authority 168 for the segment IDcontaining the data is located as described above. The host CPU 156 ofthe storage node 150 on which the non-volatile solid state storage 152and corresponding authority 168 reside requests the data from thenon-volatile solid state storage and corresponding storage nodes pointedto by the authority. In some embodiments the data is read from flashstorage as a data stripe. The host CPU 156 of storage node 150 thenreassembles the read data, correcting any errors (if present) accordingto the appropriate erasure coding scheme, and forwards the reassembleddata to the network. In further embodiments, some or all of these taskscan be handled in the non-volatile solid state storage 152. In someembodiments, the segment host requests the data be sent to storage node150 by requesting pages from storage and then sending the data to thestorage node making the original request.

In some systems, for example in UNIX-style file systems, data is handledwith an index node or inode, which specifies a data structure thatrepresents an object in a file system. The object could be a file or adirectory, for example. Metadata may accompany the object, as attributessuch as permission data and a creation timestamp, among otherattributes. A segment number could be assigned to all or a portion ofsuch an object in a file system. In other systems, data segments arehandled with a segment number assigned elsewhere. For purposes ofdiscussion, the unit of distribution is an entity, and an entity can bea file, a directory or a segment. That is, entities are units of data ormetadata stored by a storage system. Entities are grouped into setscalled authorities. Each authority has an authority owner, which is astorage node that has the exclusive right to update the entities in theauthority. In other words, a storage node contains the authority, andthat the authority, in turn, contains entities.

A segment is a logical container of data in accordance with someembodiments. A segment is an address space between medium address spaceand physical flash locations, i.e., the data segment number, are in thisaddress space. Segments may also contain meta-data, which enable dataredundancy to be restored (rewritten to different flash locations ordevices) without the involvement of higher level software. In oneembodiment, an internal format of a segment contains client data andmedium mappings to determine the position of that data. Each datasegment is protected, e.g., from memory and other failures, by breakingthe segment into a number of data and parity shards, where applicable.The data and parity shards are distributed, i.e., striped, acrossnon-volatile solid state storage 152 coupled to the host CPUs 156 (SeeFIGS. 2E and 2G) in accordance with an erasure coding scheme. Usage ofthe term segments refers to the container and its place in the addressspace of segments in some embodiments. Usage of the term stripe refersto the same set of shards as a segment and includes how the shards aredistributed along with redundancy or parity information in accordancewith some embodiments.

A series of address-space transformations takes place across an entirestorage system. At the top are the directory entries (file names) whichlink to an inode. Inodes point into medium address space, where data islogically stored. Medium addresses may be mapped through a series ofindirect mediums to spread the load of large files, or implement dataservices like deduplication or snapshots. Medium addresses may be mappedthrough a series of indirect mediums to spread the load of large files,or implement data services like deduplication or snapshots. Segmentaddresses are then translated into physical flash locations. Physicalflash locations have an address range bounded by the amount of flash inthe system in accordance with some embodiments. Medium addresses andsegment addresses are logical containers, and in some embodiments use a128 bit or larger identifier so as to be practically infinite, with alikelihood of reuse calculated as longer than the expected life of thesystem. Addresses from logical containers are allocated in ahierarchical fashion in some embodiments. Initially, each non-volatilesolid state storage unit 152 may be assigned a range of address space.Within this assigned range, the non-volatile solid state storage 152 isable to allocate addresses without synchronization with othernon-volatile solid state storage 152.

Data and metadata is stored by a set of underlying storage layouts thatare optimized for varying workload patterns and storage devices. Theselayouts incorporate multiple redundancy schemes, compression formats andindex algorithms. Some of these layouts store information aboutauthorities and authority masters, while others store file metadata andfile data. The redundancy schemes include error correction codes thattolerate corrupted bits within a single storage device (such as a NANDflash chip), erasure codes that tolerate the failure of multiple storagenodes, and replication schemes that tolerate data center or regionalfailures. In some embodiments, low density parity check (‘LDPC’) code isused within a single storage unit. Reed-Solomon encoding is used withina storage cluster, and mirroring is used within a storage grid in someembodiments. Metadata may be stored using an ordered log structuredindex (such as a Log Structured Merge Tree), and large data may not bestored in a log structured layout.

In order to maintain consistency across multiple copies of an entity,the storage nodes agree implicitly on two things through calculations:(1) the authority that contains the entity, and (2) the storage nodethat contains the authority. The assignment of entities to authoritiescan be done by pseudo randomly assigning entities to authorities, bysplitting entities into ranges based upon an externally produced key, orby placing a single entity into each authority. Examples of pseudorandomschemes are linear hashing and the Replication Under Scalable Hashing(‘RUSH’) family of hashes, including Controlled Replication UnderScalable Hashing (‘CRUSH’). In some embodiments, pseudo-randomassignment is utilized only for assigning authorities to nodes becausethe set of nodes can change. The set of authorities cannot change so anysubjective function may be applied in these embodiments. Some placementschemes automatically place authorities on storage nodes, while otherplacement schemes rely on an explicit mapping of authorities to storagenodes. In some embodiments, a pseudorandom scheme is utilized to mapfrom each authority to a set of candidate authority owners. Apseudorandom data distribution function related to CRUSH may assignauthorities to storage nodes and create a list of where the authoritiesare assigned. Each storage node has a copy of the pseudorandom datadistribution function, and can arrive at the same calculation fordistributing, and later finding or locating an authority. Each of thepseudorandom schemes requires the reachable set of storage nodes asinput in some embodiments in order to conclude the same target nodes.Once an entity has been placed in an authority, the entity may be storedon physical devices so that no expected failure will lead to unexpecteddata loss. In some embodiments, rebalancing algorithms attempt to storethe copies of all entities within an authority in the same layout and onthe same set of machines.

Examples of expected failures include device failures, stolen machines,datacenter fires, and regional disasters, such as nuclear or geologicalevents. Different failures lead to different levels of acceptable dataloss. In some embodiments, a stolen storage node impacts neither thesecurity nor the reliability of the system, while depending on systemconfiguration, a regional event could lead to no loss of data, a fewseconds or minutes of lost updates, or even complete data loss.

In the embodiments, the placement of data for storage redundancy isindependent of the placement of authorities for data consistency. Insome embodiments, storage nodes that contain authorities do not containany persistent storage. Instead, the storage nodes are connected tonon-volatile solid state storage units that do not contain authorities.The communications interconnect between storage nodes and non-volatilesolid state storage units consists of multiple communicationtechnologies and has non-uniform performance and fault tolerancecharacteristics. In some embodiments, as mentioned above, non-volatilesolid state storage units are connected to storage nodes via PCIexpress, storage nodes are connected together within a single chassisusing Ethernet backplane, and chassis are connected together to form astorage cluster. Storage clusters are connected to clients usingEthernet or fiber channel in some embodiments. If multiple storageclusters are configured into a storage grid, the multiple storageclusters are connected using the Internet or other long-distancenetworking links, such as a “metro scale” link or private link that doesnot traverse the internet.

Authority owners have the exclusive right to modify entities, to migrateentities from one non-volatile solid state storage unit to anothernon-volatile solid state storage unit, and to add and remove copies ofentities. This allows for maintaining the redundancy of the underlyingdata. When an authority owner fails, is going to be decommissioned, oris overloaded, the authority is transferred to a new storage node.Transient failures make it non-trivial to ensure that all non-faultymachines agree upon the new authority location. The ambiguity thatarises due to transient failures can be achieved automatically by aconsensus protocol such as Paxos, hot-warm failover schemes, via manualintervention by a remote system administrator, or by a local hardwareadministrator (such as by physically removing the failed machine fromthe cluster, or pressing a button on the failed machine). In someembodiments, a consensus protocol is used, and failover is automatic. Iftoo many failures or replication events occur in too short a timeperiod, the system goes into a self-preservation mode and haltsreplication and data movement activities until an administratorintervenes in accordance with some embodiments.

As authorities are transferred between storage nodes and authorityowners update entities in their authorities, the system transfersmessages between the storage nodes and non-volatile solid state storageunits. With regard to persistent messages, messages that have differentpurposes are of different types. Depending on the type of the message,the system maintains different ordering and durability guarantees. Asthe persistent messages are being processed, the messages aretemporarily stored in multiple durable and non-durable storage hardwaretechnologies. In some embodiments, messages are stored in RAM, NVRAM andon NAND flash devices, and a variety of protocols are used in order tomake efficient use of each storage medium. Latency-sensitive clientrequests may be persisted in replicated NVRAM, and then later NAND,while background rebalancing operations are persisted directly to NAND.

Persistent messages are persistently stored prior to being transmitted.This allows the system to continue to serve client requests despitefailures and component replacement. Although many hardware componentscontain unique identifiers that are visible to system administrators,manufacturer, hardware supply chain and ongoing monitoring qualitycontrol infrastructure, applications running on top of theinfrastructure address virtualize addresses. These virtualized addressesdo not change over the lifetime of the storage system, regardless ofcomponent failures and replacements. This allows each component of thestorage system to be replaced over time without reconfiguration ordisruptions of client request processing, i.e., the system supportsnon-disruptive upgrades.

In some embodiments, the virtualized addresses are stored withsufficient redundancy. A continuous monitoring system correlateshardware and software status and the hardware identifiers. This allowsdetection and prediction of failures due to faulty components andmanufacturing details. The monitoring system also enables the proactivetransfer of authorities and entities away from impacted devices beforefailure occurs by removing the component from the critical path in someembodiments.

FIG. 2C is a multiple level block diagram, showing contents of a storagenode 150 and contents of a non-volatile solid state storage 152 of thestorage node 150. Data is communicated to and from the storage node 150by a network interface controller (‘NIC’) 202 in some embodiments. Eachstorage node 150 has a CPU 156, and one or more non-volatile solid statestorage 152, as discussed above. Moving down one level in FIG. 2C, eachnon-volatile solid state storage 152 has a relatively fast non-volatilesolid state memory, such as nonvolatile random access memory (‘NVRAM’)204, and flash memory 206. In some embodiments, NVRAM 204 may be acomponent that does not require program/erase cycles (DRAM, MRAM, PCM),and can be a memory that can support being written vastly more oftenthan the memory is read from. Moving down another level in FIG. 2C, theNVRAM 204 is implemented in one embodiment as high speed volatilememory, such as dynamic random access memory (DRAM) 216, backed up byenergy reserve 218. Energy reserve 218 provides sufficient electricalpower to keep the DRAM 216 powered long enough for contents to betransferred to the flash memory 206 in the event of power failure. Insome embodiments, energy reserve 218 is a capacitor, super-capacitor,battery, or other device, that supplies a suitable supply of energysufficient to enable the transfer of the contents of DRAM 216 to astable storage medium in the case of power loss. The flash memory 206 isimplemented as multiple flash dies 222, which may be referred to aspackages of flash dies 222 or an array of flash dies 222. It should beappreciated that the flash dies 222 could be packaged in any number ofways, with a single die per package, multiple dies per package (i.e.multichip packages), in hybrid packages, as bare dies on a printedcircuit board or other substrate, as encapsulated dies, etc. In theembodiment shown, the non-volatile solid state storage 152 has acontroller 212 or other processor, and an input output (I/O) port 210coupled to the controller 212. I/O port 210 is coupled to the CPU 156and/or the network interface controller 202 of the flash storage node150. Flash input output (I/O) port 220 is coupled to the flash dies 222,and a direct memory access unit (DMA) 214 is coupled to the controller212, the DRAM 216 and the flash dies 222. In the embodiment shown, theI/O port 210, controller 212, DMA unit 214 and flash I/O port 220 areimplemented on a programmable logic device (‘PLD’) 208, e.g., a fieldprogrammable gate array (FPGA). In this embodiment, each flash die 222has pages, organized as sixteen kB (kilobyte) pages 224, and a register226 through which data can be written to or read from the flash die 222.In further embodiments, other types of solid-state memory are used inplace of, or in addition to flash memory illustrated within flash die222.

Storage clusters 161, in various embodiments as disclosed herein, can becontrasted with storage arrays in general. The storage nodes 150 arepart of a collection that creates the storage cluster 161. Each storagenode 150 owns a slice of data and computing required to provide thedata. Multiple storage nodes 150 cooperate to store and retrieve thedata. Storage memory or storage devices, as used in storage arrays ingeneral, are less involved with processing and manipulating the data.Storage memory or storage devices in a storage array receive commands toread, write, or erase data. The storage memory or storage devices in astorage array are not aware of a larger system in which they areembedded, or what the data means. Storage memory or storage devices instorage arrays can include various types of storage memory, such as RAM,solid state drives, hard disk drives, etc. The storage units 152described herein have multiple interfaces active simultaneously andserving multiple purposes. In some embodiments, some of thefunctionality of a storage node 150 is shifted into a storage unit 152,transforming the storage unit 152 into a combination of storage unit 152and storage node 150. Placing computing (relative to storage data) intothe storage unit 152 places this computing closer to the data itself.The various system embodiments have a hierarchy of storage node layerswith different capabilities. By contrast, in a storage array, acontroller owns and knows everything about all of the data that thecontroller manages in a shelf or storage devices. In a storage cluster161, as described herein, multiple controllers in multiple storage units152 and/or storage nodes 150 cooperate in various ways (e.g., forerasure coding, data sharding, metadata communication and redundancy,storage capacity expansion or contraction, data recovery, and so on).

FIG. 2D shows a storage server environment, which uses embodiments ofthe storage nodes 150 and storage units 152 of FIGS. 2A-C. In thisversion, each storage unit 152 has a processor such as controller 212(see FIG. 2C), an FPGA (field programmable gate array), flash memory206, and NVRAM 204 (which is super-capacitor backed DRAM 216, see FIGS.2B and 2C) on a PCIe (peripheral component interconnect express) boardin a chassis 138 (see FIG. 2A). The storage unit 152 may be implementedas a single board containing storage, and may be the largest tolerablefailure domain inside the chassis. In some embodiments, up to twostorage units 152 may fail and the device will continue with no dataloss.

The physical storage is divided into named regions based on applicationusage in some embodiments. The NVRAM 204 is a contiguous block ofreserved memory in the storage unit 152 DRAM 216, and is backed by NANDflash. NVRAM 204 is logically divided into multiple memory regionswritten for two as spool (e.g., spool region). Space within the NVRAM204 spools is managed by each authority 168 independently. Each deviceprovides an amount of storage space to each authority 168. Thatauthority 168 further manages lifetimes and allocations within thatspace. Examples of a spool include distributed transactions or notions.When the primary power to a storage unit 152 fails, onboardsuper-capacitors provide a short duration of power hold up. During thisholdup interval, the contents of the NVRAM 204 are flushed to flashmemory 206. On the next power-on, the contents of the NVRAM 204 arerecovered from the flash memory 206.

As for the storage unit controller, the responsibility of the logical“controller” is distributed across each of the blades containingauthorities 168. This distribution of logical control is shown in FIG.2D as a host controller 242, mid-tier controller 244 and storage unitcontroller(s) 246. Management of the control plane and the storage planeare treated independently, although parts may be physically co-locatedon the same blade. Each authority 168 effectively serves as anindependent controller. Each authority 168 provides its own data andmetadata structures, its own background workers, and maintains its ownlifecycle.

FIG. 2E is a blade 252 hardware block diagram, showing a control plane254, compute and storage planes 256, 258, and authorities 168interacting with underlying physical resources, using embodiments of thestorage nodes 150 and storage units 152 of FIGS. 2A-C in the storageserver environment of FIG. 2D. The control plane 254 is partitioned intoa number of authorities 168 which can use the compute resources in thecompute plane 256 to run on any of the blades 252. The storage plane 258is partitioned into a set of devices, each of which provides access toflash 206 and NVRAM 204 resources. In one embodiment, the compute plane256 may perform the operations of a storage array controller, asdescribed herein, on one or more devices of the storage plane 258 (e.g.,a storage array).

In the compute and storage planes 256, 258 of FIG. 2E, the authorities168 interact with the underlying physical resources (i.e., devices).From the point of view of an authority 168, its resources are stripedover all of the physical devices. From the point of view of a device, itprovides resources to all authorities 168, irrespective of where theauthorities happen to run. Each authority 168 has allocated or has beenallocated one or more partitions 260 of storage memory in the storageunits 152, e.g. partitions 260 in flash memory 206 and NVRAM 204. Eachauthority 168 uses those allocated partitions 260 that belong to it, forwriting or reading user data. Authorities can be associated withdiffering amounts of physical storage of the system. For example, oneauthority 168 could have a larger number of partitions 260 or largersized partitions 260 in one or more storage units 152 than one or moreother authorities 168.

FIG. 2F depicts elasticity software layers in blades 252 of a storagecluster, in accordance with some embodiments. In the elasticitystructure, elasticity software is symmetric, i.e., each blade's computemodule 270 runs the three identical layers of processes depicted in FIG.2F. Storage managers 274 execute read and write requests from otherblades 252 for data and metadata stored in local storage unit 152 NVRAM204 and flash 206. Authorities 168 fulfill client requests by issuingthe necessary reads and writes to the blades 252 on whose storage units152 the corresponding data or metadata resides. Endpoints 272 parseclient connection requests received from switch fabric 146 supervisorysoftware, relay the client connection requests to the authorities 168responsible for fulfillment, and relay the authorities' 168 responses toclients. The symmetric three-layer structure enables the storagesystem's high degree of concurrency. Elasticity scales out efficientlyand reliably in these embodiments. In addition, elasticity implements aunique scale-out technique that balances work evenly across allresources regardless of client access pattern, and maximizes concurrencyby eliminating much of the need for inter-blade coordination thattypically occurs with conventional distributed locking.

Still referring to FIG. 2F, authorities 168 running in the computemodules 270 of a blade 252 perform the internal operations required tofulfill client requests. One feature of elasticity is that authorities168 are stateless, i.e., they cache active data and metadata in theirown blades' 252 DRAMs for fast access, but the authorities store everyupdate in their NVRAM 204 partitions on three separate blades 252 untilthe update has been written to flash 206. All the storage system writesto NVRAM 204 are in triplicate to partitions on three separate blades252 in some embodiments. With triple-mirrored NVRAM 204 and persistentstorage protected by parity and Reed-Solomon RAID checksums, the storagesystem can survive concurrent failure of two blades 252 with no loss ofdata, metadata, or access to either.

Because authorities 168 are stateless, they can migrate between blades252. Each authority 168 has a unique identifier. NVRAM 204 and flash 206partitions are associated with authorities' 168 identifiers, not withthe blades 252 on which they are running in some. Thus, when anauthority 168 migrates, the authority 168 continues to manage the samestorage partitions from its new location. When a new blade 252 isinstalled in an embodiment of the storage cluster, the systemautomatically rebalances load by: partitioning the new blade's 252storage for use by the system's authorities 168, migrating selectedauthorities 168 to the new blade 252, starting endpoints 272 on the newblade 252 and including them in the switch fabric's 146 clientconnection distribution algorithm.

From their new locations, migrated authorities 168 persist the contentsof their NVRAM 204 partitions on flash 206, process read and writerequests from other authorities 168, and fulfill the client requeststhat endpoints 272 direct to them. Similarly, if a blade 252 fails or isremoved, the system redistributes its authorities 168 among the system'sremaining blades 252. The redistributed authorities 168 continue toperform their original functions from their new locations.

FIG. 2G depicts authorities 168 and storage resources in blades 252 of astorage cluster, in accordance with some embodiments. Each authority 168is exclusively responsible for a partition of the flash 206 and NVRAM204 on each blade 252. The authority 168 manages the content andintegrity of its partitions independently of other authorities 168.Authorities 168 compress incoming data and preserve it temporarily intheir NVRAM 204 partitions, and then consolidate, RAID-protect, andpersist the data in segments of the storage in their flash 206partitions. As the authorities 168 write data to flash 206, storagemanagers 274 perform the necessary flash translation to optimize writeperformance and maximize media longevity. In the background, authorities168 “garbage collect,” or reclaim space occupied by data that clientshave made obsolete by overwriting the data. It should be appreciatedthat since authorities' 168 partitions are disjoint, there is no needfor distributed locking to execute client and writes or to performbackground functions.

The embodiments described herein may utilize various software,communication and/or networking protocols. In addition, theconfiguration of the hardware and/or software may be adjusted toaccommodate various protocols. For example, the embodiments may utilizeActive Directory, which is a database based system that providesauthentication, directory, policy, and other services in a WINDOWS™environment. In these embodiments, LDAP (Lightweight Directory AccessProtocol) is one example application protocol for querying and modifyingitems in directory service providers such as Active Directory. In someembodiments, a network lock manager (‘NLM’) is utilized as a facilitythat works in cooperation with the Network File System (‘NFS’) toprovide a System V style of advisory file and record locking over anetwork. The Server Message Block (‘SMB’) protocol, one version of whichis also known as Common Internet File System (‘CIFS’), may be integratedwith the storage systems discussed herein. SMP operates as anapplication-layer network protocol typically used for providing sharedaccess to files, printers, and serial ports and miscellaneouscommunications between nodes on a network. SMB also provides anauthenticated inter-process communication mechanism. AMAZON™ S3 (SimpleStorage Service) is a web service offered by Amazon Web Services, andthe systems described herein may interface with Amazon S3 through webservices interfaces (REST (representational state transfer), SOAP(simple object access protocol), and BitTorrent). A RESTful API(application programming interface) breaks down a transaction to createa series of small modules. Each module addresses a particular underlyingpart of the transaction. The control or permissions provided with theseembodiments, especially for object data, may include utilization of anaccess control list (‘ACL’). The ACL is a list of permissions attachedto an object and the ACL specifies which users or system processes aregranted access to objects, as well as what operations are allowed ongiven objects. The systems may utilize Internet Protocol version 6(‘IPv6’), as well as IPv4, for the communications protocol that providesan identification and location system for computers on networks androutes traffic across the Internet. The routing of packets betweennetworked systems may include Equal-cost multi-path routing (‘ECMP’),which is a routing strategy where next-hop packet forwarding to a singledestination can occur over multiple “best paths” which tie for top placein routing metric calculations. Multi-path routing can be used inconjunction with most routing protocols, because it is a per-hopdecision limited to a single router. The software may supportMulti-tenancy, which is an architecture in which a single instance of asoftware application serves multiple customers. Each customer may bereferred to as a tenant. Tenants may be given the ability to customizesome parts of the application, but may not customize the application'scode, in some embodiments. The embodiments may maintain audit logs. Anaudit log is a document that records an event in a computing system. Inaddition to documenting what resources were accessed, audit log entriestypically include destination and source addresses, a timestamp, anduser login information for compliance with various regulations. Theembodiments may support various key management policies, such asencryption key rotation. In addition, the system may support dynamicroot passwords or some variation dynamically changing passwords.

FIG. 3A sets forth a diagram of a storage system 306 that is coupled fordata communications with a cloud services provider 302 in accordancewith some embodiments of the present disclosure. Although depicted inless detail, the storage system 306 depicted in FIG. 3A may be similarto the storage systems described above with reference to FIGS. 1A-1D andFIGS. 2A-2G. In some embodiments, the storage system 306 depicted inFIG. 3A may be embodied as a storage system that includes imbalancedactive/active controllers, as a storage system that includes balancedactive/active controllers, as a storage system that includesactive/active controllers where less than all of each controller'sresources are utilized such that each controller has reserve resourcesthat may be used to support failover, as a storage system that includesfully active/active controllers, as a storage system that includesdataset-segregated controllers, as a storage system that includesdual-layer architectures with front-end controllers and back-endintegrated storage controllers, as a storage system that includesscale-out clusters of dual-controller arrays, as well as combinations ofsuch embodiments.

In the example depicted in FIG. 3A, the storage system 306 is coupled tothe cloud services provider 302 via a data communications link 304. Thedata communications link 304 may be embodied as a dedicated datacommunications link, as a data communications pathway that is providedthrough the use of one or data communications networks such as a widearea network (‘WAN’) or local area network (‘LAN’), or as some othermechanism capable of transporting digital information between thestorage system 306 and the cloud services provider 302. Such a datacommunications link 304 may be fully wired, fully wireless, or someaggregation of wired and wireless data communications pathways. In suchan example, digital information may be exchanged between the storagesystem 306 and the cloud services provider 302 via the datacommunications link 304 using one or more data communications protocols.For example, digital information may be exchanged between the storagesystem 306 and the cloud services provider 302 via the datacommunications link 304 using the handheld device transfer protocol(‘HDTP’), hypertext transfer protocol (‘HTTP’), internet protocol(‘IP’), real-time transfer protocol (‘RTP’), transmission controlprotocol (‘TCP’), user datagram protocol (‘UDP’), wireless applicationprotocol (‘WAP’), or other protocol.

The cloud services provider 302 depicted in FIG. 3A may be embodied, forexample, as a system and computing environment that provides services tousers of the cloud services provider 302 through the sharing ofcomputing resources via the data communications link 304. The cloudservices provider 302 may provide on-demand access to a shared pool ofconfigurable computing resources such as computer networks, servers,storage, applications and services, and so on. The shared pool ofconfigurable resources may be rapidly provisioned and released to a userof the cloud services provider 302 with minimal management effort.Generally, the user of the cloud services provider 302 is unaware of theexact computing resources utilized by the cloud services provider 302 toprovide the services. Although in many cases such a cloud servicesprovider 302 may be accessible via the Internet, readers of skill in theart will recognize that any system that abstracts the use of sharedresources to provide services to a user through any data communicationslink may be considered a cloud services provider 302.

In the example depicted in FIG. 3A, the cloud services provider 302 maybe configured to provide a variety of services to the storage system 306and users of the storage system 306 through the implementation ofvarious service models. For example, the cloud services provider 302 maybe configured to provide services to the storage system 306 and users ofthe storage system 306 through the implementation of an infrastructureas a service (‘IaaS’) service model where the cloud services provider302 offers computing infrastructure such as virtual machines and otherresources as a service to subscribers. In addition, the cloud servicesprovider 302 may be configured to provide services to the storage system306 and users of the storage system 306 through the implementation of aplatform as a service (‘PaaS’) service model where the cloud servicesprovider 302 offers a development environment to application developers.Such a development environment may include, for example, an operatingsystem, programming-language execution environment, database, webserver, or other components that may be utilized by applicationdevelopers to develop and run software solutions on a cloud platform.Furthermore, the cloud services provider 302 may be configured toprovide services to the storage system 306 and users of the storagesystem 306 through the implementation of a software as a service(‘SaaS’) service model where the cloud services provider 302 offersapplication software, databases, as well as the platforms that are usedto run the applications to the storage system 306 and users of thestorage system 306, providing the storage system 306 and users of thestorage system 306 with on-demand software and eliminating the need toinstall and run the application on local computers, which may simplifymaintenance and support of the application. The cloud services provider302 may be further configured to provide services to the storage system306 and users of the storage system 306 through the implementation of anauthentication as a service (‘AaaS’) service model where the cloudservices provider 302 offers authentication services that can be used tosecure access to applications, data sources, or other resources. Thecloud services provider 302 may also be configured to provide servicesto the storage system 306 and users of the storage system 306 throughthe implementation of a storage as a service model where the cloudservices provider 302 offers access to its storage infrastructure foruse by the storage system 306 and users of the storage system 306.Readers will appreciate that the cloud services provider 302 may beconfigured to provide additional services to the storage system 306 andusers of the storage system 306 through the implementation of additionalservice models, as the service models described above are included onlyfor explanatory purposes and in no way represent a limitation of theservices that may be offered by the cloud services provider 302 or alimitation as to the service models that may be implemented by the cloudservices provider 302.

In the example depicted in FIG. 3A, the cloud services provider 302 maybe embodied, for example, as a private cloud, as a public cloud, or as acombination of a private cloud and public cloud. In an embodiment inwhich the cloud services provider 302 is embodied as a private cloud,the cloud services provider 302 may be dedicated to providing servicesto a single organization rather than providing services to multipleorganizations. In an embodiment where the cloud services provider 302 isembodied as a public cloud, the cloud services provider 302 may provideservices to multiple organizations. Public cloud and private clouddeployment models may differ and may come with various advantages anddisadvantages. For example, because a public cloud deployment involvesthe sharing of a computing infrastructure across different organization,such a deployment may not be ideal for organizations with securityconcerns, mission-critical workloads, uptime requirements demands, andso on. While a private cloud deployment can address some of theseissues, a private cloud deployment may require on-premises staff tomanage the private cloud. In still alternative embodiments, the cloudservices provider 302 may be embodied as a mix of a private and publiccloud services with a hybrid cloud deployment.

Although not explicitly depicted in FIG. 3A, readers will appreciatethat additional hardware components and additional software componentsmay be necessary to facilitate the delivery of cloud services to thestorage system 306 and users of the storage system 306. For example, thestorage system 306 may be coupled to (or even include) a cloud storagegateway. Such a cloud storage gateway may be embodied, for example, ashardware-based or software-based appliance that is located on premisewith the storage system 306. Such a cloud storage gateway may operate asa bridge between local applications that are executing on the storagearray 306 and remote, cloud-based storage that is utilized by thestorage array 306. Through the use of a cloud storage gateway,organizations may move primary iSCSI or NAS to the cloud servicesprovider 302, thereby enabling the organization to save space on theiron-premises storage systems. Such a cloud storage gateway may beconfigured to emulate a disk array, a block-based device, a file server,or other storage system that can translate the SCSI commands, fileserver commands, or other appropriate command into REST-space protocolsthat facilitate communications with the cloud services provider 302.

In order to enable the storage system 306 and users of the storagesystem 306 to make use of the services provided by the cloud servicesprovider 302, a cloud migration process may take place during whichdata, applications, or other elements from an organization's localsystems (or even from another cloud environment) are moved to the cloudservices provider 302. In order to successfully migrate data,applications, or other elements to the cloud services provider's 302environment, middleware such as a cloud migration tool may be utilizedto bridge gaps between the cloud services provider's 302 environment andan organization's environment. Such cloud migration tools may also beconfigured to address potentially high network costs and long transfertimes associated with migrating large volumes of data to the cloudservices provider 302, as well as addressing security concernsassociated with sensitive data to the cloud services provider 302 overdata communications networks. In order to further enable the storagesystem 306 and users of the storage system 306 to make use of theservices provided by the cloud services provider 302, a cloudorchestrator may also be used to arrange and coordinate automated tasksin pursuit of creating a consolidated process or workflow. Such a cloudorchestrator may perform tasks such as configuring various components,whether those components are cloud components or on-premises components,as well as managing the interconnections between such components. Thecloud orchestrator can simplify the inter-component communication andconnections to ensure that links are correctly configured andmaintained.

In the example depicted in FIG. 3A, and as described briefly above, thecloud services provider 302 may be configured to provide services to thestorage system 306 and users of the storage system 306 through the usageof a SaaS service model where the cloud services provider 302 offersapplication software, databases, as well as the platforms that are usedto run the applications to the storage system 306 and users of thestorage system 306, providing the storage system 306 and users of thestorage system 306 with on-demand software and eliminating the need toinstall and run the application on local computers, which may simplifymaintenance and support of the application. Such applications may takemany forms in accordance with various embodiments of the presentdisclosure. For example, the cloud services provider 302 may beconfigured to provide access to data analytics applications to thestorage system 306 and users of the storage system 306. Such dataanalytics applications may be configured, for example, to receivetelemetry data phoned home by the storage system 306. Such telemetrydata may describe various operating characteristics of the storagesystem 306 and may be analyzed, for example, to determine the health ofthe storage system 306, to identify workloads that are executing on thestorage system 306, to predict when the storage system 306 will run outof various resources, to recommend configuration changes, hardware orsoftware upgrades, workflow migrations, or other actions that mayimprove the operation of the storage system 306.

The cloud services provider 302 may also be configured to provide accessto virtualized computing environments to the storage system 306 andusers of the storage system 306. Such virtualized computing environmentsmay be embodied, for example, as a virtual machine or other virtualizedcomputer hardware platforms, virtual storage devices, virtualizedcomputer network resources, and so on. Examples of such virtualizedenvironments can include virtual machines that are created to emulate anactual computer, virtualized desktop environments that separate alogical desktop from a physical machine, virtualized file systems thatallow uniform access to different types of concrete file systems, andmany others.

For further explanation, FIG. 3B sets forth a diagram of a storagesystem 306 in accordance with some embodiments of the presentdisclosure. Although depicted in less detail, the storage system 306depicted in FIG. 3B may be similar to the storage systems describedabove with reference to FIGS. 1A-1D and FIGS. 2A-2G as the storagesystem may include many of the components described above.

The storage system 306 depicted in FIG. 3B may include storage resources308, which may be embodied in many forms. For example, in someembodiments the storage resources 308 can include nano-RAM or anotherform of nonvolatile random access memory that utilizes carbon nanotubesdeposited on a substrate. In some embodiments, the storage resources 308may include 3D crosspoint non-volatile memory in which bit storage isbased on a change of bulk resistance, in conjunction with a stackablecross-gridded data access array. In some embodiments, the storageresources 308 may include flash memory, including single-level cell(‘SLC’) NAND flash, multi-level cell (‘MLC’) NAND flash, triple-levelcell (‘TLC’) NAND flash, quad-level cell (‘QLC’) NAND flash, and others.In some embodiments, the storage resources 308 may include non-volatilemagnetoresistive random-access memory (‘MRAM’), including spin transfertorque (‘STT’) MRAM, in which data is stored through the use of magneticstorage elements. In some embodiments, the example storage resources 308may include non-volatile phase-change memory (‘PCM’) that may have theability to hold multiple bits in a single cell as cells can achieve anumber of distinct intermediary states. In some embodiments, the storageresources 308 may include quantum memory that allows for the storage andretrieval of photonic quantum information. In some embodiments, theexample storage resources 308 may include resistive random-access memory(‘ReRAM’) in which data is stored by changing the resistance across adielectric solid-state material. In some embodiments, the storageresources 308 may include storage class memory (‘SCM’) in whichsolid-state nonvolatile memory may be manufactured at a high densityusing some combination of sub-lithographic patterning techniques,multiple bits per cell, multiple layers of devices, and so on. Readerswill appreciate that other forms of computer memories and storagedevices may be utilized by the storage systems described above,including DRAM, SRAM, EEPROM, universal memory, and many others. Thestorage resources 308 depicted in FIG. 3A may be embodied in a varietyof form factors, including but not limited to, dual in-line memorymodules (‘DIMMs’), non-volatile dual in-line memory modules (‘NVDIMMs’),M.2, U.2, and others.

The storage resources 308 depicted in FIG. 3A may include various formsof storage-class memory (‘SCM’). SCM may effectively treat fast,non-volatile memory (e.g., NAND flash) as an extension of DRAM such thatan entire dataset may be treated as an in-memory dataset that residesentirely in DRAM. SCM may include non-volatile media such as, forexample, NAND flash. Such NAND flash may be accessed utilizing NVMe thatcan use the PCIe bus as its transport, providing for relatively lowaccess latencies compared to older protocols. In fact, the networkprotocols used for SSDs in all-flash arrays can include NVMe usingEthernet (ROCE, NVME TCP), Fibre Channel (NVMe FC), InfiniBand (iWARP),and others that make it possible to treat fast, non-volatile memory asan extension of DRAM. In view of the fact that DRAM is oftenbyte-addressable and fast, non-volatile memory such as NAND flash isblock-addressable, a controller software/hardware stack may be needed toconvert the block data to the bytes that are stored in the media.Examples of media and software that may be used as SCM can include, forexample, 3D XPoint, Intel Memory Drive Technology, Samsung's Z-SSD, andothers.

The example storage system 306 depicted in FIG. 3B may implement avariety of storage architectures. For example, storage systems inaccordance with some embodiments of the present disclosure may utilizeblock storage where data is stored in blocks, and each block essentiallyacts as an individual hard drive. Storage systems in accordance withsome embodiments of the present disclosure may utilize object storage,where data is managed as objects. Each object may include the dataitself, a variable amount of metadata, and a globally unique identifier,where object storage can be implemented at multiple levels (e.g., devicelevel, system level, interface level). Storage systems in accordancewith some embodiments of the present disclosure utilize file storage inwhich data is stored in a hierarchical structure. Such data may be savedin files and folders, and presented to both the system storing it andthe system retrieving it in the same format.

The example storage system 306 depicted in FIG. 3B may be embodied as astorage system in which additional storage resources can be addedthrough the use of a scale-up model, additional storage resources can beadded through the use of a scale-out model, or through some combinationthereof. In a scale-up model, additional storage may be added by addingadditional storage devices. In a scale-out model, however, additionalstorage nodes may be added to a cluster of storage nodes, where suchstorage nodes can include additional processing resources, additionalnetworking resources, and so on.

The storage system 306 depicted in FIG. 3B also includes communicationsresources 310 that may be useful in facilitating data communicationsbetween components within the storage system 306, as well as datacommunications between the storage system 306 and computing devices thatare outside of the storage system 306. The communications resources 310may be configured to utilize a variety of different protocols and datacommunication fabrics to facilitate data communications betweencomponents within the storage systems as well as computing devices thatare outside of the storage system. For example, the communicationsresources 310 can include fibre channel (‘FC’) technologies such as FCfabrics and FC protocols that can transport SCSI commands over FCnetworks. The communications resources 310 can also include FC overethernet (‘FCoE’) technologies through which FC frames are encapsulatedand transmitted over Ethernet networks. The communications resources 310can also include InfiniBand (‘IB’) technologies in which a switchedfabric topology is utilized to facilitate transmissions between channeladapters. The communications resources 310 can also include NVM Express(‘NVMe’) technologies and NVMe over fabrics (‘NVMeoF’) technologiesthrough which non-volatile storage media attached via a PCI express(‘PCIe’) bus may be accessed. The communications resources 310 can alsoinclude mechanisms for accessing storage resources 308 within thestorage system 306 utilizing serial attached SCSI (‘SAS’), serial ATA(‘SATA’) bus interfaces for connecting storage resources 308 within thestorage system 306 to host bus adapters within the storage system 306,internet small computer systems interface (‘iSCSI’) technologies toprovide block-level access to storage resources 308 within the storagesystem 306, and other communications resources that that may be usefulin facilitating data communications between components within thestorage system 306, as well as data communications between the storagesystem 306 and computing devices that are outside of the storage system306.

The storage system 306 depicted in FIG. 3B also includes processingresources 312 that may be useful in useful in executing computer programinstructions and performing other computational tasks within the storagesystem 306. The processing resources 312 may include one or moreapplication-specific integrated circuits (‘ASICs’) that are customizedfor some particular purpose as well as one or more central processingunits (‘CPUs’). The processing resources 312 may also include one ormore digital signal processors (‘DSPs’), one or more field-programmablegate arrays (‘FPGAs’), one or more systems on a chip (‘SoCs’), or otherform of processing resources 312. The storage system 306 may utilize thestorage resources 312 to perform a variety of tasks including, but notlimited to, supporting the execution of software resources 314 that willbe described in greater detail below.

The storage system 306 depicted in FIG. 3B also includes softwareresources 314 that, when executed by processing resources 312 within thestorage system 306, may perform various tasks. The software resources314 may include, for example, one or more modules of computer programinstructions that when executed by processing resources 312 within thestorage system 306 are useful in carrying out various data protectiontechniques to preserve the integrity of data that is stored within thestorage systems. Readers will appreciate that such data protectiontechniques may be carried out, for example, by system software executingon computer hardware within the storage system, by a cloud servicesprovider, or in other ways. Such data protection techniques can include,for example, data archiving techniques that cause data that is no longeractively used to be moved to a separate storage device or separatestorage system for long-term retention, data backup techniques throughwhich data stored in the storage system may be copied and stored in adistinct location to avoid data loss in the event of equipment failureor some other form of catastrophe with the storage system, datareplication techniques through which data stored in the storage systemis replicated to another storage system such that the data may beaccessible via multiple storage systems, data snapshotting techniquesthrough which the state of data within the storage system is captured atvarious points in time, data and database cloning techniques throughwhich duplicate copies of data and databases may be created, and otherdata protection techniques. Through the use of such data protectiontechniques, business continuity and disaster recovery objectives may bemet as a failure of the storage system may not result in the loss ofdata stored in the storage system.

The software resources 314 may also include software that is useful inimplementing software-defined storage (‘SDS’). In such an example, thesoftware resources 314 may include one or more modules of computerprogram instructions that, when executed, are useful in policy-basedprovisioning and management of data storage that is independent of theunderlying hardware. Such software resources 314 may be useful inimplementing storage virtualization to separate the storage hardwarefrom the software that manages the storage hardware.

The software resources 314 may also include software that is useful infacilitating and optimizing I/O operations that are directed to thestorage resources 308 in the storage system 306. For example, thesoftware resources 314 may include software modules that perform carryout various data reduction techniques such as, for example, datacompression, data deduplication, and others. The software resources 314may include software modules that intelligently group together I/Ooperations to facilitate better usage of the underlying storage resource308, software modules that perform data migration operations to migratefrom within a storage system, as well as software modules that performother functions. Such software resources 314 may be embodied as one ormore software containers or in many other ways.

Readers will appreciate that the presence of such software resources 314may provide for an improved user experience of the storage system 306,an expansion of functionality supported by the storage system 306, andmany other benefits. Consider the specific example of the softwareresources 314 carrying out data backup techniques through which datastored in the storage system may be copied and stored in a distinctlocation to avoid data loss in the event of equipment failure or someother form of catastrophe. In such an example, the systems describedherein may more reliably (and with less burden placed on the user)perform backup operations relative to interactive backup managementsystems that require high degrees of user interactivity, offer lessrobust automation and feature sets, and so on.

For further explanation, FIG. 3C sets forth an example of a cloud-basedstorage system 318 in accordance with some embodiments of the presentdisclosure. In the example depicted in FIG. 3C, the cloud-based storagesystem 318 is created entirely in a cloud computing environment 316 suchas, for example, Amazon Web Services (‘AWS’), Microsoft Azure, GoogleCloud Platform, IBM Cloud, Oracle Cloud, and others. The cloud-basedstorage system 318 may be used to provide services similar to theservices that may be provided by the storage systems described above.For example, the cloud-based storage system 318 may be used to provideblock storage services to users of the cloud-based storage system 318,the cloud-based storage system 318 may be used to provide storageservices to users of the cloud-based storage system 318 through the useof solid-state storage, and so on.

The cloud-based storage system 318 depicted in FIG. 3C includes twocloud computing instances 320, 322 that each are used to support theexecution of a storage controller application 324, 326. The cloudcomputing instances 320, 322 may be embodied, for example, as instancesof cloud computing resources (e.g., virtual machines) that may beprovided by the cloud computing environment 316 to support the executionof software applications such as the storage controller application 324,326. In one embodiment, the cloud computing instances 320, 322 may beembodied as Amazon Elastic Compute Cloud (‘EC2’) instances. In such anexample, an Amazon Machine Image (‘AMI’) that includes the storagecontroller application 324, 326 may be booted to create and configure avirtual machine that may execute the storage controller application 324,326.

In the example method depicted in FIG. 3C, the storage controllerapplication 324, 326 may be embodied as a module of computer programinstructions that, when executed, carries out various storage tasks. Forexample, the storage controller application 324, 326 may be embodied asa module of computer program instructions that, when executed, carriesout the same tasks as the controllers 110A, 110B in FIG. 1A describedabove such as writing data received from the users of the cloud-basedstorage system 318 to the cloud-based storage system 318, erasing datafrom the cloud-based storage system 318, retrieving data from thecloud-based storage system 318 and providing such data to users of thecloud-based storage system 318, monitoring and reporting of diskutilization and performance, performing redundancy operations, such asRAID or RAID-like data redundancy operations, compressing data,encrypting data, deduplicating data, and so forth. Readers willappreciate that because there are two cloud computing instances 320, 322that each include the storage controller application 324, 326, in someembodiments one cloud computing instance 320 may operate as the primarycontroller as described above while the other cloud computing instance322 may operate as the secondary controller as described above. In suchan example, in order to save costs, the cloud computing instance 320that operates as the primary controller may be deployed on a relativelyhigh-performance and relatively expensive cloud computing instance whilethe cloud computing instance 322 that operates as the secondarycontroller may be deployed on a relatively low-performance andrelatively inexpensive cloud computing instance. Readers will appreciatethat the storage controller application 324, 326 depicted in FIG. 3C mayinclude identical source code that is executed within different cloudcomputing instances 320, 322.

Consider an example in which the cloud computing environment 316 isembodied as AWS and the cloud computing instances are embodied as EC2instances. In such an example, AWS offers many types of EC2 instances.For example, AWS offers a suite of general purpose EC2 instances thatinclude varying levels of memory and processing power. In such anexample, the cloud computing instance 320 that operates as the primarycontroller may be deployed on one of the instance types that has arelatively large amount of memory and processing power while the cloudcomputing instance 322 that operates as the secondary controller may bedeployed on one of the instance types that has a relatively small amountof memory and processing power. In such an example, upon the occurrenceof a failover event where the roles of primary and secondary areswitched, a double failover may actually be carried out such that: 1) afirst failover event where the cloud computing instance 322 thatformerly operated as the secondary controller begins to operate as theprimary controller, and 2) a third cloud computing instance (not shown)that is of an instance type that has a relatively large amount of memoryand processing power is spun up with a copy of the storage controllerapplication, where the third cloud computing instance begins operatingas the primary controller while the cloud computing instance 322 thatoriginally operated as the secondary controller begins operating as thesecondary controller again. In such an example, the cloud computinginstance 320 that formerly operated as the primary controller may beterminated. Readers will appreciate that in alternative embodiments, thecloud computing instance 320 that is operating as the secondarycontroller after the failover event may continue to operate as thesecondary controller and the cloud computing instance 322 that operatedas the primary controller after the occurrence of the failover event maybe terminated once the primary role has been assumed by the third cloudcomputing instance (not shown).

Readers will appreciate that while the embodiments described aboverelate to embodiments where one cloud computing instance 320 operates asthe primary controller and the second cloud computing instance 322operates as the secondary controller, other embodiments are within thescope of the present disclosure. For example, each cloud computinginstance 320, 322 may operate as a primary controller for some portionof the address space supported by the cloud-based storage system 318,each cloud computing instance 320, 322 may operate as a primarycontroller where the servicing of I/O operations directed to thecloud-based storage system 318 are divided in some other way, and so on.In fact, in other embodiments where costs savings may be prioritizedover performance demands, only a single cloud computing instance mayexist that contains the storage controller application. In such anexample, a controller failure may take more time to recover from as anew cloud computing instance that includes the storage controllerapplication would need to be spun up rather than having an alreadycreated cloud computing instance take on the role of servicing I/Ooperations that would have otherwise been handled by the failed cloudcomputing instance.

The cloud-based storage system 318 depicted in FIG. 3C includes cloudcomputing instances 340 a, 340 b, 340 n with local storage 330, 334,338. The cloud computing instances 340 a, 340 b, 340 n depicted in FIG.3C may be embodied, for example, as instances of cloud computingresources that may be provided by the cloud computing environment 316 tosupport the execution of software applications. The cloud computinginstances 340 a, 340 b, 340 n of FIG. 3C may differ from the cloudcomputing instances 320, 322 described above as the cloud computinginstances 340 a, 340 b, 340 n of FIG. 3C have local storage 330, 334,338 resources whereas the cloud computing instances 320, 322 thatsupport the execution of the storage controller application 324, 326need not have local storage resources. The cloud computing instances 340a, 340 b, 340 n with local storage 330, 334, 338 may be embodied, forexample, as EC2 M5 instances that include one or more SSDs, as EC2 R5instances that include one or more SSDs, as EC2 I3 instances thatinclude one or more SSDs, and so on. In some embodiments, the localstorage 330, 334, 338 must be embodied as solid-state storage (e.g.,SSDs) rather than storage that makes use of hard disk drives.

In the example depicted in FIG. 3C, each of the cloud computinginstances 340 a, 340 b, 340 n with local storage 330, 334, 338 caninclude a software daemon 328, 332, 336 that, when executed by a cloudcomputing instance 340 a, 340 b, 340 n can present itself to the storagecontroller applications 324, 326 as if the cloud computing instance 340a, 340 b, 340 n were a physical storage device (e.g., one or more SSDs).In such an example, the software daemon 328, 332, 336 may includecomputer program instructions similar to those that would normally becontained on a storage device such that the storage controllerapplications 324, 326 can send and receive the same commands that astorage controller would send to storage devices. In such a way, thestorage controller applications 324, 326 may include code that isidentical to (or substantially identical to) the code that would beexecuted by the controllers in the storage systems described above. Inthese and similar embodiments, communications between the storagecontroller applications 324, 326 and the cloud computing instances 340a, 340 b, 340 n with local storage 330, 334, 338 may utilize iSCSI, NVMeover TCP, messaging, a custom protocol, or in some other mechanism.

In the example depicted in FIG. 3C, each of the cloud computinginstances 340 a, 340 b, 340 n with local storage 330, 334, 338 may alsobe coupled to block-storage 342, 344, 346 that is offered by the cloudcomputing environment 316. The block-storage 342, 344, 346 that isoffered by the cloud computing environment 316 may be embodied, forexample, as Amazon Elastic Block Store (‘EBS’) volumes. For example, afirst EBS volume may be coupled to a first cloud computing instance 340a, a second EBS volume may be coupled to a second cloud computinginstance 340 b, and a third EBS volume may be coupled to a third cloudcomputing instance 340 n. In such an example, the block-storage 342,344, 346 that is offered by the cloud computing environment 316 may beutilized in a manner that is similar to how the NVRAM devices describedabove are utilized, as the software daemon 328, 332, 336 (or some othermodule) that is executing within a particular cloud comping instance 340a, 340 b, 340 n may, upon receiving a request to write data, initiate awrite of the data to its attached EBS volume as well as a write of thedata to its local storage 330, 334, 338 resources. In some alternativeembodiments, data may only be written to the local storage 330, 334, 338resources within a particular cloud comping instance 340 a, 340 b, 340n. In an alternative embodiment, rather than using the block-storage342, 344, 346 that is offered by the cloud computing environment 316 asNVRAM, actual RAM on each of the cloud computing instances 340 a, 340 b,340 n with local storage 330, 334, 338 may be used as NVRAM, therebydecreasing network utilization costs that would be associated with usingan EBS volume as the NVRAM.

In the example depicted in FIG. 3C, the cloud computing instances 340 a,340 b, 340 n with local storage 330, 334, 338 may be utilized, by cloudcomputing instances 320, 322 that support the execution of the storagecontroller application 324, 326 to service I/O operations that aredirected to the cloud-based storage system 318. Consider an example inwhich a first cloud computing instance 320 that is executing the storagecontroller application 324 is operating as the primary controller. Insuch an example, the first cloud computing instance 320 that isexecuting the storage controller application 324 may receive (directlyor indirectly via the secondary controller) requests to write data tothe cloud-based storage system 318 from users of the cloud-based storagesystem 318. In such an example, the first cloud computing instance 320that is executing the storage controller application 324 may performvarious tasks such as, for example, deduplicating the data contained inthe request, compressing the data contained in the request, determiningwhere to the write the data contained in the request, and so on, beforeultimately sending a request to write a deduplicated, encrypted, orotherwise possibly updated version of the data to one or more of thecloud computing instances 340 a, 340 b, 340 n with local storage 330,334, 338. Either cloud computing instance 320, 322, in some embodiments,may receive a request to read data from the cloud-based storage system318 and may ultimately send a request to read data to one or more of thecloud computing instances 340 a, 340 b, 340 n with local storage 330,334, 338.

Readers will appreciate that when a request to write data is received bya particular cloud computing instance 340 a, 340 b, 340 n with localstorage 330, 334, 338, the software daemon 328, 332, 336 or some othermodule of computer program instructions that is executing on theparticular cloud computing instance 340 a, 340 b, 340 n may beconfigured to not only write the data to its own local storage 330, 334,338 resources and any appropriate block-storage 342, 344, 346 that areoffered by the cloud computing environment 316, but the software daemon328, 332, 336 or some other module of computer program instructions thatis executing on the particular cloud computing instance 340 a, 340 b,340 n may also be configured to write the data to cloud-based objectstorage 348 that is attached to the particular cloud computing instance340 a, 340 b, 340 n. The cloud-based object storage 348 that is attachedto the particular cloud computing instance 340 a, 340 b, 340 n may beembodied, for example, as Amazon Simple Storage Service (‘S3’) storagethat is accessible by the particular cloud computing instance 340 a, 340b, 340 n. In other embodiments, the cloud computing instances 320, 322that each include the storage controller application 324, 326 mayinitiate the storage of the data in the local storage 330, 334, 338 ofthe cloud computing instances 340 a, 340 b, 340 n and the cloud-basedobject storage 348.

Readers will appreciate that, as described above, the cloud-basedstorage system 318 may be used to provide block storage services tousers of the cloud-based storage system 318. While the local storage330, 334, 338 resources and the block-storage 342, 344, 346 resourcesthat are utilized by the cloud computing instances 340 a, 340 b, 340 nmay support block-level access, the cloud-based object storage 348 thatis attached to the particular cloud computing instance 340 a, 340 b, 340n supports only object-based access. In order to address this, thesoftware daemon 328, 332, 336 or some other module of computer programinstructions that is executing on the particular cloud computinginstance 340 a, 340 b, 340 n may be configured to take blocks of data,package those blocks into objects, and write the objects to thecloud-based object storage 348 that is attached to the particular cloudcomputing instance 340 a, 340 b, 340 n.

Consider an example in which data is written to the local storage 330,334, 338 resources and the block-storage 342, 344, 346 resources thatare utilized by the cloud computing instances 340 a, 340 b, 340 n in 1MB blocks. In such an example, assume that a user of the cloud-basedstorage system 318 issues a request to write data that, after beingcompressed and deduplicated by the storage controller application 324,326 results in the need to write 5 MB of data. In such an example,writing the data to the local storage 330, 334, 338 resources and theblock-storage 342, 344, 346 resources that are utilized by the cloudcomputing instances 340 a, 340 b, 340 n is relatively straightforward as5 blocks that are 1 MB in size are written to the local storage 330,334, 338 resources and the block-storage 342, 344, 346 resources thatare utilized by the cloud computing instances 340 a, 340 b, 340 n. Insuch an example, the software daemon 328, 332, 336 or some other moduleof computer program instructions that is executing on the particularcloud computing instance 340 a, 340 b, 340 n may be configured to: 1)create a first object that includes the first 1 MB of data and write thefirst object to the cloud-based object storage 348, 2) create a secondobject that includes the second 1 MB of data and write the second objectto the cloud-based object storage 348, 3) create a third object thatincludes the third 1 MB of data and write the third object to thecloud-based object storage 348, and so on. As such, in some embodiments,each object that is written to the cloud-based object storage 348 may beidentical (or nearly identical) in size. Readers will appreciate that insuch an example, metadata that is associated with the data itself may beincluded in each object (e.g., the first 1 MB of the object is data andthe remaining portion is metadata associated with the data).

Readers will appreciate that the cloud-based object storage 348 may beincorporated into the cloud-based storage system 318 to increase thedurability of the cloud-based storage system 318. Continuing with theexample described above where the cloud computing instances 340 a, 340b, 340 n are EC2 instances, readers will understand that EC2 instancesare only guaranteed to have a monthly uptime of 99.9% and data stored inthe local instance store only persists during the lifetime of the EC2instance. As such, relying on the cloud computing instances 340 a, 340b, 340 n with local storage 330, 334, 338 as the only source ofpersistent data storage in the cloud-based storage system 318 may resultin a relatively unreliable storage system. Likewise, EBS volumes aredesigned for 99.999% availability. As such, even relying on EBS as thepersistent data store in the cloud-based storage system 318 may resultin a storage system that is not sufficiently durable. Amazon S3,however, is designed to provide 99.999999999% durability, meaning that acloud-based storage system 318 that can incorporate S3 into its pool ofstorage is substantially more durable than various other options.

Readers will appreciate that while a cloud-based storage system 318 thatcan incorporate S3 into its pool of storage is substantially moredurable than various other options, utilizing S3 as the primary pool ofstorage may result in storage system that has relatively slow responsetimes and relatively long I/O latencies. As such, the cloud-basedstorage system 318 depicted in FIG. 3C not only stores data in S3 butthe cloud-based storage system 318 also stores data in local storage330, 334, 338 resources and block-storage 342, 344, 346 resources thatare utilized by the cloud computing instances 340 a, 340 b, 340 n, suchthat read operations can be serviced from local storage 330, 334, 338resources and the block-storage 342, 344, 346 resources that areutilized by the cloud computing instances 340 a, 340 b, 340 n, therebyreducing read latency when users of the cloud-based storage system 318attempt to read data from the cloud-based storage system 318.

In some embodiments, all data that is stored by the cloud-based storagesystem 318 may be stored in both: 1) the cloud-based object storage 348,and 2) at least one of the local storage 330, 334, 338 resources orblock-storage 342, 344, 346 resources that are utilized by the cloudcomputing instances 340 a, 340 b, 340 n. In such embodiments, the localstorage 330, 334, 338 resources and block-storage 342, 344, 346resources that are utilized by the cloud computing instances 340 a, 340b, 340 n may effectively operate as cache that generally includes alldata that is also stored in S3, such that all reads of data may beserviced by the cloud computing instances 340 a, 340 b, 340 n withoutrequiring the cloud computing instances 340 a, 340 b, 340 n to accessthe cloud-based object storage 348. Readers will appreciate that inother embodiments, however, all data that is stored by the cloud-basedstorage system 318 may be stored in the cloud-based object storage 348,but less than all data that is stored by the cloud-based storage system318 may be stored in at least one of the local storage 330, 334, 338resources or block-storage 342, 344, 346 resources that are utilized bythe cloud computing instances 340 a, 340 b, 340 n. In such an example,various policies may be utilized to determine which subset of the datathat is stored by the cloud-based storage system 318 should reside inboth: 1) the cloud-based object storage 348, and 2) at least one of thelocal storage 330, 334, 338 resources or block-storage 342, 344, 346resources that are utilized by the cloud computing instances 340 a, 340b, 340 n.

As described above, when the cloud computing instances 340 a, 340 b, 340n with local storage 330, 334, 338 are embodied as EC2 instances, thecloud computing instances 340 a, 340 b, 340 n with local storage 330,334, 338 are only guaranteed to have a monthly uptime of 99.9% and datastored in the local instance store only persists during the lifetime ofeach cloud computing instance 340 a, 340 b, 340 n with local storage330, 334, 338. As such, one or more modules of computer programinstructions that are executing within the cloud-based storage system318 (e.g., a monitoring module that is executing on its own EC2instance) may be designed to handle the failure of one or more of thecloud computing instances 340 a, 340 b, 340 n with local storage 330,334, 338. In such an example, the monitoring module may handle thefailure of one or more of the cloud computing instances 340 a, 340 b,340 n with local storage 330, 334, 338 by creating one or more new cloudcomputing instances with local storage, retrieving data that was storedon the failed cloud computing instances 340 a, 340 b, 340 n from thecloud-based object storage 348, and storing the data retrieved from thecloud-based object storage 348 in local storage on the newly createdcloud computing instances. Readers will appreciate that many variants ofthis process may be implemented.

Consider an example in which all cloud computing instances 340 a, 340 b,340 n with local storage 330, 334, 338 failed. In such an example, themonitoring module may create new cloud computing instances with localstorage, where high-bandwidth instances types are selected that allowfor the maximum data transfer rates between the newly createdhigh-bandwidth cloud computing instances with local storage and thecloud-based object storage 348. Readers will appreciate that instancestypes are selected that allow for the maximum data transfer ratesbetween the new cloud computing instances and the cloud-based objectstorage 348 such that the new high-bandwidth cloud computing instancescan be rehydrated with data from the cloud-based object storage 348 asquickly as possible. Once the new high-bandwidth cloud computinginstances are rehydrated with data from the cloud-based object storage348, less expensive lower-bandwidth cloud computing instances may becreated, data may be migrated to the less expensive lower-bandwidthcloud computing instances, and the high-bandwidth cloud computinginstances may be terminated.

Readers will appreciate that in some embodiments, the number of newcloud computing instances that are created may substantially exceed thenumber of cloud computing instances that are needed to locally store allof the data stored by the cloud-based storage system 318. The number ofnew cloud computing instances that are created may substantially exceedthe number of cloud computing instances that are needed to locally storeall of the data stored by the cloud-based storage system 318 in order tomore rapidly pull data from the cloud-based object storage 348 and intothe new cloud computing instances, as each new cloud computing instancecan (in parallel) retrieve some portion of the data stored by thecloud-based storage system 318. In such embodiments, once the datastored by the cloud-based storage system 318 has been pulled into thenewly created cloud computing instances, the data may be consolidatedwithin a subset of the newly created cloud computing instances and thosenewly created cloud computing instances that are excessive may beterminated.

Consider an example in which 1000 cloud computing instances are neededin order to locally store all valid data that users of the cloud-basedstorage system 318 have written to the cloud-based storage system 318.In such an example, assume that all 1,000 cloud computing instancesfail. In such an example, the monitoring module may cause 100,000 cloudcomputing instances to be created, where each cloud computing instanceis responsible for retrieving, from the cloud-based object storage 348,distinct 1/100,000th chunks of the valid data that users of thecloud-based storage system 318 have written to the cloud-based storagesystem 318 and locally storing the distinct chunk of the dataset that itretrieved. In such an example, because each of the 100,000 cloudcomputing instances can retrieve data from the cloud-based objectstorage 348 in parallel, the caching layer may be restored 100 timesfaster as compared to an embodiment where the monitoring module onlycreate 1000 replacement cloud computing instances. In such an example,over time the data that is stored locally in the 100,000 could beconsolidated into 1,000 cloud computing instances and the remaining99,000 cloud computing instances could be terminated.

Readers will appreciate that various performance aspects of thecloud-based storage system 318 may be monitored (e.g., by a monitoringmodule that is executing in an EC2 instance) such that the cloud-basedstorage system 318 can be scaled-up or scaled-out as needed. Consider anexample in which the monitoring module monitors the performance of thecloud-based storage system 318 via communications with one or more ofthe cloud computing instances 320, 322 that each are used to support theexecution of a storage controller application 324, 326, via monitoringcommunications between cloud computing instances 320, 322, 340 a, 340 b,340 n, via monitoring communications between cloud computing instances320, 322, 340 a, 340 b, 340 n and the cloud-based object storage 348, orin some other way. In such an example, assume that the monitoring moduledetermines that the cloud computing instances 320, 322 that are used tosupport the execution of a storage controller application 324, 326 areundersized and not sufficiently servicing the I/O requests that areissued by users of the cloud-based storage system 318. In such anexample, the monitoring module may create a new, more powerful cloudcomputing instance (e.g., a cloud computing instance of a type thatincludes more processing power, more memory, etc . . . ) that includesthe storage controller application such that the new, more powerfulcloud computing instance can begin operating as the primary controller.Likewise, if the monitoring module determines that the cloud computinginstances 320, 322 that are used to support the execution of a storagecontroller application 324, 326 are oversized and that cost savingscould be gained by switching to a smaller, less powerful cloud computinginstance, the monitoring module may create a new, less powerful (andless expensive) cloud computing instance that includes the storagecontroller application such that the new, less powerful cloud computinginstance can begin operating as the primary controller.

Consider, as an additional example of dynamically sizing the cloud-basedstorage system 318, an example in which the monitoring module determinesthat the utilization of the local storage that is collectively providedby the cloud computing instances 340 a, 340 b, 340 n has reached apredetermined utilization threshold (e.g., 95%). In such an example, themonitoring module may create additional cloud computing instances withlocal storage to expand the pool of local storage that is offered by thecloud computing instances. Alternatively, the monitoring module maycreate one or more new cloud computing instances that have largeramounts of local storage than the already existing cloud computinginstances 340 a, 340 b, 340 n, such that data stored in an alreadyexisting cloud computing instance 340 a, 340 b, 340 n can be migrated tothe one or more new cloud computing instances and the already existingcloud computing instance 340 a, 340 b, 340 n can be terminated, therebyexpanding the pool of local storage that is offered by the cloudcomputing instances. Likewise, if the pool of local storage that isoffered by the cloud computing instances is unnecessarily large, datacan be consolidated and some cloud computing instances can beterminated.

Readers will appreciate that the cloud-based storage system 318 may besized up and down automatically by a monitoring module applying apredetermined set of rules that may be relatively simple of relativelycomplicated. In fact, the monitoring module may not only take intoaccount the current state of the cloud-based storage system 318, but themonitoring module may also apply predictive policies that are based on,for example, observed behavior (e.g., every night from 10 PM until 6 AMusage of the storage system is relatively light), predeterminedfingerprints (e.g., every time a virtual desktop infrastructure adds 100virtual desktops, the number of IOPS directed to the storage systemincrease by X), and so on. In such an example, the dynamic scaling ofthe cloud-based storage system 318 may be based on current performancemetrics, predicted workloads, and many other factors, includingcombinations thereof.

Readers will further appreciate that because the cloud-based storagesystem 318 may be dynamically scaled, the cloud-based storage system 318may even operate in a way that is more dynamic. Consider the example ofgarbage collection. In a traditional storage system, the amount ofstorage is fixed. As such, at some point the storage system may beforced to perform garbage collection as the amount of available storagehas become so constrained that the storage system is on the verge ofrunning out of storage. In contrast, the cloud-based storage system 318described here can always ‘add’ additional storage (e.g., by adding morecloud computing instances with local storage). Because the cloud-basedstorage system 318 described here can always ‘add’ additional storage,the cloud-based storage system 318 can make more intelligent decisionsregarding when to perform garbage collection. For example, thecloud-based storage system 318 may implement a policy that garbagecollection only be performed when the number of IOPS being serviced bythe cloud-based storage system 318 falls below a certain level. In someembodiments, other system-level functions (e.g., deduplication,compression) may also be turned off and on in response to system load,given that the size of the cloud-based storage system 318 is notconstrained in the same way that traditional storage systems areconstrained.

Readers will appreciate that embodiments of the present disclosureresolve an issue with block-storage services offered by some cloudcomputing environments as some cloud computing environments only allowfor one cloud computing instance to connect to a block-storage volume ata single time. For example, in Amazon AWS, only a single EC2 instancemay be connected to an EBS volume. Through the use of EC2 instances withlocal storage, embodiments of the present disclosure can offermulti-connect capabilities where multiple EC2 instances can connect toanother EC2 instance with local storage (‘a drive instance’). In suchembodiments, the drive instances may include software executing withinthe drive instance that allows the drive instance to support I/Odirected to a particular volume from each connected EC2 instance. Assuch, some embodiments of the present disclosure may be embodied asmulti-connect block storage services that may not include all of thecomponents depicted in FIG. 3C.

In some embodiments, especially in embodiments where the cloud-basedobject storage 348 resources are embodied as Amazon S3, the cloud-basedstorage system 318 may include one or more modules (e.g., a module ofcomputer program instructions executing on an EC2 instance) that areconfigured to ensure that when the local storage of a particular cloudcomputing instance is rehydrated with data from S3, the appropriate datais actually in S3. This issue arises largely because S3 implements aneventual consistency model where, when overwriting an existing object,reads of the object will eventually (but not necessarily immediately)become consistent and will eventually (but not necessarily immediately)return the overwritten version of the object. To address this issue, insome embodiments of the present disclosure, objects in S3 are neveroverwritten. Instead, a traditional ‘overwrite’ would result in thecreation of the new object (that includes the updated version of thedata) and the eventual deletion of the old object (that includes theprevious version of the data).

In some embodiments of the present disclosure, as part of an attempt tonever (or almost never) overwrite an object, when data is written to S3the resultant object may be tagged with a sequence number. In someembodiments, these sequence numbers may be persisted elsewhere (e.g., ina database) such that at any point in time, the sequence numberassociated with the most up-to-date version of some piece of data can beknown. In such a way, a determination can be made as to whether S3 hasthe most recent version of some piece of data by merely reading thesequence number associated with an object—and without actually readingthe data from S3. The ability to make this determination may beparticularly important when a cloud computing instance with localstorage crashes, as it would be undesirable to rehydrate the localstorage of a replacement cloud computing instance with out-of-date data.In fact, because the cloud-based storage system 318 does not need toaccess the data to verify its validity, the data can stay encrypted andaccess charges can be avoided.

The storage systems described above may carry out intelligent databackup techniques through which data stored in the storage system may becopied and stored in a distinct location to avoid data loss in the eventof equipment failure or some other form of catastrophe. For example, thestorage systems described above may be configured to examine each backupto avoid restoring the storage system to an undesirable state. Consideran example in which malware infects the storage system. In such anexample, the storage system may include software resources 314 that canscan each backup to identify backups that were captured before themalware infected the storage system and those backups that were capturedafter the malware infected the storage system. In such an example, thestorage system may restore itself from a backup that does not includethe malware—or at least not restore the portions of a backup thatcontained the malware. In such an example, the storage system mayinclude software resources 314 that can scan each backup to identify thepresences of malware (or a virus, or some other undesirable), forexample, by identifying write operations that were serviced by thestorage system and originated from a network subnet that is suspected tohave delivered the malware, by identifying write operations that wereserviced by the storage system and originated from a user that issuspected to have delivered the malware, by identifying write operationsthat were serviced by the storage system and examining the content ofthe write operation against fingerprints of the malware, and in manyother ways.

Readers will further appreciate that the backups (often in the form ofone or more snapshots) may also be utilized to perform rapid recovery ofthe storage system. Consider an example in which the storage system isinfected with ransomware that locks users out of the storage system. Insuch an example, software resources 314 within the storage system may beconfigured to detect the presence of ransomware and may be furtherconfigured to restore the storage system to a point-in-time, using theretained backups, prior to the point-in-time at which the ransomwareinfected the storage system. In such an example, the presence ofransomware may be explicitly detected through the use of software toolsutilized by the system, through the use of a key (e.g., a USB drive)that is inserted into the storage system, or in a similar way. Likewise,the presence of ransomware may be inferred in response to systemactivity meeting a predetermined fingerprint such as, for example, noreads or writes coming into the system for a predetermined period oftime.

Readers will appreciate that the various components depicted in FIG. 3Bmay be grouped into one or more optimized computing packages asconverged infrastructures. Such converged infrastructures may includepools of computers, storage and networking resources that can be sharedby multiple applications and managed in a collective manner usingpolicy-driven processes. Such converged infrastructures may minimizecompatibility issues between various components within the storagesystem 306 while also reducing various costs associated with theestablishment and operation of the storage system 306. Such convergedinfrastructures may be implemented with a converged infrastructurereference architecture, with standalone appliances, with a softwaredriven hyper-converged approach (e.g., hyper-converged infrastructures),or in other ways.

Readers will appreciate that the storage system 306 depicted in FIG. 3Bmay be useful for supporting various types of software applications. Forexample, the storage system 306 may be useful in supporting artificialintelligence (‘AI’) applications, database applications, DevOpsprojects, electronic design automation tools, event-driven softwareapplications, high performance computing applications, simulationapplications, high-speed data capture and analysis applications, machinelearning applications, media production applications, media servingapplications, picture archiving and communication systems (‘PACS’)applications, software development applications, virtual realityapplications, augmented reality applications, and many other types ofapplications by providing storage resources to such applications.

The storage systems described above may operate to support a widevariety of applications. In view of the fact that the storage systemsinclude compute resources, storage resources, and a wide variety ofother resources, the storage systems may be well suited to supportapplications that are resource intensive such as, for example, AIapplications. Such AI applications may enable devices to perceive theirenvironment and take actions that maximize their chance of success atsome goal. Examples of such AI applications can include IBM Watson,Microsoft Oxford, Google DeepMind, Baidu Minwa, and others. The storagesystems described above may also be well suited to support other typesof applications that are resource intensive such as, for example,machine learning applications. Machine learning applications may performvarious types of data analysis to automate analytical model building.Using algorithms that iteratively learn from data, machine learningapplications can enable computers to learn without being explicitlyprogrammed. One particular area of machine learning is referred to asreinforcement learning, which involves taking suitable actions tomaximize reward in a particular situation. Reinforcement learning may beemployed to find the best possible behavior or path that a particularsoftware application or machine should take in a specific situation.Reinforcement learning differs from other areas of machine learning(e.g., supervised learning, unsupervised learning) in that correctinput/output pairs need not be presented for reinforcement learning andsub-optimal actions need not be explicitly corrected.

In addition to the resources already described, the storage systemsdescribed above may also include graphics processing units (‘GPUs’),occasionally referred to as visual processing unit (‘VPUs’). Such GPUsmay be embodied as specialized electronic circuits that rapidlymanipulate and alter memory to accelerate the creation of images in aframe buffer intended for output to a display device. Such GPUs may beincluded within any of the computing devices that are part of thestorage systems described above, including as one of many individuallyscalable components of a storage system, where other examples ofindividually scalable components of such storage system can includestorage components, memory components, compute components (e.g., CPUs,FPGAs, ASICs), networking components, software components, and others.In addition to GPUs, the storage systems described above may alsoinclude neural network processors (‘NNPs’) for use in various aspects ofneural network processing. Such NNPs may be used in place of (or inaddition to) GPUs and may also be independently scalable.

As described above, the storage systems described herein may beconfigured to support artificial intelligence applications, machinelearning applications, big data analytics applications, and many othertypes of applications. The rapid growth in these sort of applications isbeing driven by three technologies: deep learning (DL), GPU processors,and Big Data. Deep learning is a computing model that makes use ofmassively parallel neural networks inspired by the human brain. Insteadof experts handcrafting software, a deep learning model writes its ownsoftware by learning from lots of examples. A GPU is a modern processorwith thousands of cores, well-suited to run algorithms that looselyrepresent the parallel nature of the human brain.

Advances in deep neural networks have ignited a new wave of algorithmsand tools for data scientists to tap into their data with artificialintelligence (AI). With improved algorithms, larger data sets, andvarious frameworks (including open-source software libraries for machinelearning across a range of tasks), data scientists are tackling new usecases like autonomous driving vehicles, natural language processing andunderstanding, computer vision, machine reasoning, strong AI, and manyothers. Applications of such techniques may include: machine andvehicular object detection, identification and avoidance; visualrecognition, classification and tagging; algorithmic financial tradingstrategy performance management; simultaneous localization and mapping;predictive maintenance of high-value machinery; prevention against cybersecurity threats, expertise automation; image recognition andclassification; question answering; robotics; text analytics(extraction, classification) and text generation and translation; andmany others. Applications of AI techniques has materialized in a widearray of products include, for example, Amazon Echo's speech recognitiontechnology that allows users to talk to their machines, GoogleTranslate™ which allows for machine-based language translation,Spotify's Discover Weekly that provides recommendations on new songs andartists that a user may like based on the user's usage and trafficanalysis, Quill's text generation offering that takes structured dataand turns it into narrative stories, Chatbots that provide real-time,contextually specific answers to questions in a dialog format, and manyothers. Furthermore, AI may impact a wide variety of industries andsectors. For example, AI solutions may be used in healthcare to takeclinical notes, patient files, research data, and other inputs togenerate potential treatment options for doctors to explore. Likewise,AI solutions may be used by retailers to personalize consumerrecommendations based on a person's digital footprint of behaviors,profile data, or other data.

Training deep neural networks, however, requires both high quality inputdata and large amounts of computation. GPUs are massively parallelprocessors capable of operating on large amounts of data simultaneously.When combined into a multi-GPU cluster, a high throughput pipeline maybe required to feed input data from storage to the compute engines. Deeplearning is more than just constructing and training models. There alsoexists an entire data pipeline that must be designed for the scale,iteration, and experimentation necessary for a data science team tosucceed.

Data is the heart of modern AI and deep learning algorithms. Beforetraining can begin, one problem that must be addressed revolves aroundcollecting the labeled data that is crucial for training an accurate AImodel. A full scale AI deployment may be required to continuouslycollect, clean, transform, label, and store large amounts of data.Adding additional high quality data points directly translates to moreaccurate models and better insights. Data samples may undergo a seriesof processing steps including, but not limited to: 1) ingesting the datafrom an external source into the training system and storing the data inraw form, 2) cleaning and transforming the data in a format convenientfor training, including linking data samples to the appropriate label,3) exploring parameters and models, quickly testing with a smallerdataset, and iterating to converge on the most promising models to pushinto the production cluster, 4) executing training phases to selectrandom batches of input data, including both new and older samples, andfeeding those into production GPU servers for computation to updatemodel parameters, and 5) evaluating including using a holdback portionof the data not used in training in order to evaluate model accuracy onthe holdout data. This lifecycle may apply for any type of parallelizedmachine learning, not just neural networks or deep learning. Forexample, standard machine learning frameworks may rely on CPUs insteadof GPUs but the data ingest and training workflows may be the same.Readers will appreciate that a single shared storage data hub creates acoordination point throughout the lifecycle without the need for extradata copies among the ingest, preprocessing, and training stages. Rarelyis the ingested data used for only one purpose, and shared storage givesthe flexibility to train multiple different models or apply traditionalanalytics to the data.

Readers will appreciate that each stage in the AI data pipeline may havevarying requirements from the data hub (e.g., the storage system orcollection of storage systems). Scale-out storage systems must deliveruncompromising performance for all manner of access types andpatterns—from small, metadata-heavy to large files, from random tosequential access patterns, and from low to high concurrency. Thestorage systems described above may serve as an ideal AI data hub as thesystems may service unstructured workloads. In the first stage, data isideally ingested and stored on to the same data hub that followingstages will use, in order to avoid excess data copying. The next twosteps can be done on a standard compute server that optionally includesa GPU, and then in the fourth and last stage, full training productionjobs are run on powerful GPU-accelerated servers. Often, there is aproduction pipeline alongside an experimental pipeline operating on thesame dataset. Further, the GPU-accelerated servers can be usedindependently for different models or joined together to train on onelarger model, even spanning multiple systems for distributed training.If the shared storage tier is slow, then data must be copied to localstorage for each phase, resulting in wasted time staging data ontodifferent servers. The ideal data hub for the AI training pipelinedelivers performance similar to data stored locally on the server nodewhile also having the simplicity and performance to enable all pipelinestages to operate concurrently.

A data scientist works to improve the usefulness of the trained modelthrough a wide variety of approaches: more data, better data, smartertraining, and deeper models. In many cases, there will be teams of datascientists sharing the same datasets and working in parallel to producenew and improved training models. Often, there is a team of datascientists working within these phases concurrently on the same shareddatasets. Multiple, concurrent workloads of data processing,experimentation, and full-scale training layer the demands of multipleaccess patterns on the storage tier. In other words, storage cannot justsatisfy large file reads, but must contend with a mix of large and smallfile reads and writes. Finally, with multiple data scientists exploringdatasets and models, it may be critical to store data in its nativeformat to provide flexibility for each user to transform, clean, and usethe data in a unique way. The storage systems described above mayprovide a natural shared storage home for the dataset, with dataprotection redundancy (e.g., by using RAID6) and the performancenecessary to be a common access point for multiple developers andmultiple experiments. Using the storage systems described above mayavoid the need to carefully copy subsets of the data for local work,saving both engineering and GPU-accelerated servers use time. Thesecopies become a constant and growing tax as the raw data set and desiredtransformations constantly update and change.

Readers will appreciate that a fundamental reason why deep learning hasseen a surge in success is the continued improvement of models withlarger data set sizes. In contrast, classical machine learningalgorithms, like logistic regression, stop improving in accuracy atsmaller data set sizes. As such, the separation of compute resources andstorage resources may also allow independent scaling of each tier,avoiding many of the complexities inherent in managing both together. Asthe data set size grows or new data sets are considered, a scale outstorage system must be able to expand easily. Similarly, if moreconcurrent training is required, additional GPUs or other computeresources can be added without concern for their internal storage.Furthermore, the storage systems described above may make building,operating, and growing an AI system easier due to the random readbandwidth provided by the storage systems, the ability to of the storagesystems to randomly read small files (50 KB) high rates (meaning that noextra effort is required to aggregate individual data points to makelarger, storage-friendly files), the ability of the storage systems toscale capacity and performance as either the dataset grows or thethroughput requirements grow, the ability of the storage systems tosupport files or objects, the ability of the storage systems to tuneperformance for large or small files (i.e., no need for the user toprovision filesystems), the ability of the storage systems to supportnon-disruptive upgrades of hardware and software even during productionmodel training, and for many other reasons.

Small file performance of the storage tier may be critical as many typesof inputs, including text, audio, or images will be natively stored assmall files. If the storage tier does not handle small files well, anextra step will be required to pre-process and group samples into largerfiles. Storage, built on top of spinning disks, that relies on SSD as acaching tier, may fall short of the performance needed. Because trainingwith random input batches results in more accurate models, the entiredata set must be accessible with full performance. SSD caches onlyprovide high performance for a small subset of the data and will beineffective at hiding the latency of spinning drives.

Although the preceding paragraphs discuss deep learning applications,readers will appreciate that the storage systems described herein mayalso be part of a distributed deep learning (‘DDL’) platform to supportthe execution of DDL algorithms. Distributed deep learning may can beused to significantly accelerate deep learning with distributedcomputing on GPUs (or other form of accelerator or computer programinstruction executor), such that parallelism can be achieved. Inaddition, the output of training machine learning and deep learningmodels, such as a fully trained machine learning model, may be used fora variety of purposes and in conjunction with other tools. For example,trained machine learning models may be used in conjunction with toolslike Core ML to integrate a broad variety of machine learning modeltypes into an application. In fact, trained models may be run throughCore ML converter tools and inserted into a custom application that canbe deployed on compatible devices. The storage systems described abovemay also be paired with other technologies such as TensorFlow, anopen-source software library for dataflow programming across a range oftasks that may be used for machine learning applications such as neuralnetworks, to facilitate the development of such machine learning models,applications, and so on.

Readers will further appreciate that the systems described above may bedeployed in a variety of ways to support the democratization of AI, asAI becomes more available for mass consumption. The democratization ofAI may include, for example, the ability to offer AI as aPlatform-as-a-Service, the growth of Artificial general intelligenceofferings, the proliferation of Autonomous level 4 and Autonomous level5 vehicles, the availability of autonomous mobile robots, thedevelopment of conversational AI platforms, and many others. Forexample, the systems described above may be deployed in cloudenvironments, edge environments, or other environments that are usefulin supporting the democratization of AI. As part of the democratizationof AI, a movement may occur from narrow AI that consists of highlyscoped machine learning solutions that target a particular task toartificial general intelligence where the use of machine learning isexpanded to handle a broad range of use cases that could essentiallyperform any intelligent task that a human could perform and could learndynamically, much like a human.

The storage systems described above may also be used in a neuromorphiccomputing environment. Neuromorphic computing is a form of computingthat mimics brain cells. To support neuromorphic computing, anarchitecture of interconnected “neurons” replace traditional computingmodels with low-powered signals that go directly between neurons formore efficient computation. Neuromorphic computing may make use ofvery-large-scale integration (VLSI) systems containing electronic analogcircuits to mimic neuro-biological architectures present in the nervoussystem, as well as analog, digital, mixed-mode analog/digital VLSI, andsoftware systems that implement models of neural systems for perception,motor control, or multisensory integration.

Readers will appreciate that the storage systems described above may beconfigured to support the storage or use of (among other types of data)blockchains. Such blockchains may be embodied as a continuously growinglist of records, called blocks, which are linked and secured usingcryptography. Each block in a blockchain may contain a hash pointer as alink to a previous block, a timestamp, transaction data, and so on.Blockchains may be designed to be resistant to modification of the dataand can serve as an open, distributed ledger that can recordtransactions between two parties efficiently and in a verifiable andpermanent way. This makes blockchains potentially suitable for therecording of events, medical records, and other records managementactivities, such as identity management, transaction processing, andothers. In addition to supporting the storage and use of blockchaintechnologies, the storage systems described above may also support thestorage and use of derivative items such as, for example, open sourceblockchains and related tools that are part of the IBM™ Hyperledgerproject, permissioned blockchains in which a certain number of trustedparties are allowed to access the block chain, blockchain products thatenable developers to build their own distributed ledger projects, andothers. Readers will appreciate that blockchain technologies may impacta wide variety of industries and sectors. For example, blockchaintechnologies may be used in real estate transactions as blockchain basedcontracts whose use can eliminate the need for 3^(rd) parties and enableself-executing actions when conditions are met. Likewise, universalhealth records can be created by aggregating and placing a person'shealth history onto a blockchain ledger for any healthcare provider, orpermissioned health care providers, to access and update.

Readers will appreciate that the usage of blockchains is not limited tofinancial transactions, contracts, and the like. In fact, blockchainsmay be leveraged to enable the decentralized aggregation, ordering,timestamping and archiving of any type of information, includingstructured data, correspondence, documentation, or other data. Throughthe usage of blockchains, participants can provably and permanentlyagree on exactly what data was entered, when and by whom, withoutrelying on a trusted intermediary. For example, SAP's recently launchedblockchain platform, which supports MultiChain and Hyperledger Fabric,targets a broad range of supply chain and other non-financialapplications.

One way to use a blockchain for recording data is to embed each piece ofdata directly inside a transaction. Every blockchain transaction may bedigitally signed by one or more parties, replicated to a plurality ofnodes, ordered and timestamped by the chain's consensus algorithm, andstored permanently in a tamper-proof way. Any data within thetransaction will therefore be stored identically but independently byevery node, along with a proof of who wrote it and when. The chain'susers are able to retrieve this information at any future time. Thistype of storage may be referred to as on-chain storage. On-chain storagemay not be particularly practical, however, when attempting to store avery large dataset. As such, in accordance with embodiments of thepresent disclosure, blockchains and the storage systems described hereinmay be leveraged to support on-chain storage of data as well asoff-chain storage of data.

Off-chain storage of data can be implemented in a variety of ways andcan occur when the data itself is not stored within the blockchain. Forexample, in one embodiment, a hash function may be utilized and the dataitself may be fed into the hash function to generate a hash value. Insuch an example, the hashes of large pieces of data may be embeddedwithin transactions, instead of the data itself. Each hash may serve asa commitment to its input data, with the data itself being storedoutside of the blockchain. Readers will appreciate that any blockchainparticipant that needs an off-chain piece of data cannot reproduce thedata from its hash, but if the data can be retrieved in some other way,then the on-chain hash serves to confirm who created it and when. Justlike regular on-chain data, the hash may be embedded inside a digitallysigned transaction, which was included in the chain by consensus.

Readers will appreciate that, in other embodiments, alternatives toblockchains may be used to facilitate the decentralized storage ofinformation. For example, one alternative to a blockchain that may beused is a blockweave. While conventional blockchains store everytransaction to achieve validation, a blockweave permits securedecentralization without the usage of the entire chain, thereby enablinglow cost on-chain storage of data. Such blockweaves may utilize aconsensus mechanism that is based on proof of access (PoA) and proof ofwork (PoW). While typical PoW systems only depend on the previous blockin order to generate each successive block, the PoA algorithm mayincorporate data from a randomly chosen previous block. Combined withthe blockweave data structure, miners do not need to store all blocks(forming a blockchain), but rather can store any previous blocks forminga weave of blocks (a blockweave). This enables increased levels ofscalability, speed and low-cost and reduces the cost of data storage inpart because miners need not store all blocks, thereby resulting in asubstantial reduction in the amount of electricity that is consumedduring the mining process because, as the network expands, electricityconsumption decreases because a blockweave demands less and less hashingpower for consensus as data is added to the system. Furthermore,blockweaves may be deployed on a decentralized storage network in whichincentives are created to encourage rapid data sharing. Suchdecentralized storage networks may also make use of blockshadowingtechniques, where nodes only send a minimal block “shadow” to othernodes that allows peers to reconstruct a full block, instead oftransmitting the full block itself.

The storage systems described above may, either alone or in combinationwith other computing devices, be used to support in-memory computingapplications. In memory computing involves the storage of information inRAM that is distributed across a cluster of computers. In-memorycomputing helps business customers, including retailers, banks andutilities, to quickly detect patterns, analyze massive data volumes onthe fly, and perform their operations quickly. Readers will appreciatethat the storage systems described above, especially those that areconfigurable with customizable amounts of processing resources, storageresources, and memory resources (e.g., those systems in which bladesthat contain configurable amounts of each type of resource), may beconfigured in a way so as to provide an infrastructure that can supportin-memory computing. Likewise, the storage systems described above mayinclude component parts (e.g., NVDIMMs, 3D crosspoint storage thatprovide fast random access memory that is persistent) that can actuallyprovide for an improved in-memory computing environment as compared toin-memory computing environments that rely on RAM distributed acrossdedicated servers.

In some embodiments, the storage systems described above may beconfigured to operate as a hybrid in-memory computing environment thatincludes a universal interface to all storage media (e.g., RAM, flashstorage, 3D crosspoint storage). In such embodiments, users may have noknowledge regarding the details of where their data is stored but theycan still use the same full, unified API to address data. In suchembodiments, the storage system may (in the background) move data to thefastest layer available—including intelligently placing the data independence upon various characteristics of the data or in dependenceupon some other heuristic. In such an example, the storage systems mayeven make use of existing products such as Apache Ignite and GridGain tomove data between the various storage layers, or the storage systems maymake use of custom software to move data between the various storagelayers. The storage systems described herein may implement variousoptimizations to improve the performance of in-memory computing such as,for example, having computations occur as close to the data as possible.

Readers will further appreciate that in some embodiments, the storagesystems described above may be paired with other resources to supportthe applications described above. For example, one infrastructure couldinclude primary compute in the form of servers and workstations whichspecialize in using General-purpose computing on graphics processingunits (‘GPGPU’) to accelerate deep learning applications that areinterconnected into a computation engine to train parameters for deepneural networks. Each system may have Ethernet external connectivity,InfiniBand external connectivity, some other form of externalconnectivity, or some combination thereof. In such an example, the GPUscan be grouped for a single large training or used independently totrain multiple models. The infrastructure could also include a storagesystem such as those described above to provide, for example, ascale-out all-flash file or object store through which data can beaccessed via high-performance protocols such as NFS, S3, and so on. Theinfrastructure can also include, for example, redundant top-of-rackEthernet switches connected to storage and compute via ports in MLAGport channels for redundancy. The infrastructure could also includeadditional compute in the form of whitebox servers, optionally withGPUs, for data ingestion, pre-processing, and model debugging. Readerswill appreciate that additional infrastructures are also be possible.

Readers will appreciate that the systems described above may be bettersuited for the applications described above relative to other systemsthat may include, for example, a distributed direct-attached storage(DDAS) solution deployed in server nodes. Such DDAS solutions may bebuilt for handling large, less sequential accesses but may be less ableto handle small, random accesses. Readers will further appreciate thatthe storage systems described above may be utilized to provide aplatform for the applications described above that is preferable to theutilization of cloud-based resources as the storage systems may beincluded in an on-site or in-house infrastructure that is more secure,more locally and internally managed, more robust in feature sets andperformance, or otherwise preferable to the utilization of cloud-basedresources as part of a platform to support the applications describedabove. For example, services built on platforms such as IBM's Watson mayrequire a business enterprise to distribute individual user information,such as financial transaction information or identifiable patientrecords, to other institutions. As such, cloud-based offerings of AI asa service may be less desirable than internally managed and offered AIas a service that is supported by storage systems such as the storagesystems described above, for a wide array of technical reasons as wellas for various business reasons.

Readers will appreciate that the storage systems described above, eitheralone or in coordination with other computing machinery may beconfigured to support other AI related tools. For example, the storagesystems may make use of tools like ONXX or other open neural networkexchange formats that make it easier to transfer models written indifferent AI frameworks. Likewise, the storage systems may be configuredto support tools like Amazon's Gluon that allow developers to prototype,build, and train deep learning models. In fact, the storage systemsdescribed above may be part of a larger platform, such as IBM™ CloudPrivate for Data, that includes integrated data science, dataengineering and application building services. Such platforms mayseamlessly collect, organize, secure, and analyze data across anenterprise, as well as simplify hybrid data management, unified datagovernance and integration, data science and business analytics with asingle solution.

Readers will further appreciate that the storage systems described abovemay also be deployed as an edge solution. Such an edge solution may bein place to optimize cloud computing systems by performing dataprocessing at the edge of the network, near the source of the data. Edgecomputing can push applications, data and computing power (i.e.,services) away from centralized points to the logical extremes of anetwork. Through the use of edge solutions such as the storage systemsdescribed above, computational tasks may be performed using the computeresources provided by such storage systems, data may be storage usingthe storage resources of the storage system, and cloud-based servicesmay be accessed through the use of various resources of the storagesystem (including networking resources). By performing computationaltasks on the edge solution, storing data on the edge solution, andgenerally making use of the edge solution, the consumption of expensivecloud-based resources may be avoided and, in fact, performanceimprovements may be experienced relative to a heavier reliance oncloud-based resources.

While many tasks may benefit from the utilization of an edge solution,some particular uses may be especially suited for deployment in such anenvironment. For example, devices like drones, autonomous cars, robots,and others may require extremely rapid processing—so fast, in fact, thatsending data up to a cloud environment and back to receive dataprocessing support may simply be too slow. Likewise, machines likelocomotives and gas turbines that generate large amounts of informationthrough the use of a wide array of data-generating sensors may benefitfrom the rapid data processing capabilities of an edge solution. As anadditional example, some IoT devices such as connected video cameras maynot be well-suited for the utilization of cloud-based resources as itmay be impractical (not only from a privacy perspective, securityperspective, or a financial perspective) to send the data to the cloudsimply because of the pure volume of data that is involved. As such,many tasks that really on data processing, storage, or communicationsmay be better suited by platforms that include edge solutions such asthe storage systems described above.

Consider a specific example of inventory management in a warehouse,distribution center, or similar location. A large inventory,warehousing, shipping, order-fulfillment, manufacturing or otheroperation has a large amount of inventory on inventory shelves, and highresolution digital cameras that produce a firehose of large data. All ofthis data may be taken into an image processing system, which may reducethe amount of data to a firehose of small data. All of the small datamay be stored on-premises in storage. The on-premises storage, at theedge of the facility, may be coupled to the cloud, for external reports,real-time control and cloud storage. Inventory management may beperformed with the results of the image processing, so that inventorycan be tracked on the shelves and restocked, moved, shipped, modifiedwith new products, or discontinued/obsolescent products deleted, etc.The above scenario is a prime candidate for an embodiment of theconfigurable processing and storage systems described above. Acombination of compute-only blades and offload blades suited for theimage processing, perhaps with deep learning on offload-FPGA oroffload-custom blade(s) could take in the firehose of large data fromall of the digital cameras, and produce the firehose of small data. Allof the small data could then be stored by storage nodes, operating withstorage units in whichever combination of types of storage blades besthandles the data flow. This is an example of storage and functionacceleration and integration. Depending on external communication needswith the cloud, and external processing in the cloud, and depending onreliability of network connections and cloud resources, the system couldbe sized for storage and compute management with bursty workloads andvariable conductivity reliability. Also, depending on other inventorymanagement aspects, the system could be configured for scheduling andresource management in a hybrid edge/cloud environment.

The storage systems described above may alone, or in combination withother computing resources, serves as a network edge platform thatcombines compute resources, storage resources, networking resources,cloud technologies and network virtualization technologies, and so on.As part of the network, the edge may take on characteristics similar toother network facilities, from the customer premise and backhaulaggregation facilities to Points of Presence (PoPs) and regional datacenters. Readers will appreciate that network workloads, such as VirtualNetwork Functions (VNFs) and others, will reside on the network edgeplatform. Enabled by a combination of containers and virtual machines,the network edge platform may rely on controllers and schedulers thatare no longer geographically co-located with the data processingresources. The functions, as microservices, may split into controlplanes, user and data planes, or even state machines, allowing forindependent optimization and scaling techniques to be applied. Such userand data planes may be enabled through increased accelerators, boththose residing in server platforms, such as FPGAs and Smart NICs, andthrough SDN-enabled merchant silicon and programmable ASICs.

The storage systems described above may also be optimized for use in bigdata analytics. Big data analytics may be generally described as theprocess of examining large and varied data sets to uncover hiddenpatterns, unknown correlations, market trends, customer preferences andother useful information that can help organizations make more-informedbusiness decisions. Big data analytics applications enable datascientists, predictive modelers, statisticians and other analyticsprofessionals to analyze growing volumes of structured transaction data,plus other forms of data that are often left untapped by conventionalbusiness intelligence (BI) and analytics programs. As part of thatprocess, semi-structured and unstructured data such as, for example,internet clickstream data, web server logs, social media content, textfrom customer emails and survey responses, mobile-phone call-detailrecords, IoT sensor data, and other data may be converted to astructured form. Big data analytics is a form of advanced analytics,which involves complex applications with elements such as predictivemodels, statistical algorithms and what-if analyses powered byhigh-performance analytics systems.

The storage systems described above may also support (includingimplementing as a system interface) applications that perform tasks inresponse to human speech. For example, the storage systems may supportthe execution intelligent personal assistant applications such as, forexample, Amazon's Alexa, Apple Siri, Google Voice, Samsung Bixby,Microsoft Cortana, and others. While the examples described in theprevious sentence make use of voice as input, the storage systemsdescribed above may also support chatbots, talkbots, chatterbots, orartificial conversational entities or other applications that areconfigured to conduct a conversation via auditory or textual methods.Likewise, the storage system may actually execute such an application toenable a user such as a system administrator to interact with thestorage system via speech. Such applications are generally capable ofvoice interaction, music playback, making to-do lists, setting alarms,streaming podcasts, playing audiobooks, and providing weather, traffic,and other real time information, such as news, although in embodimentsin accordance with the present disclosure, such applications may beutilized as interfaces to various system management operations.

The storage systems described above may also implement AI platforms fordelivering on the vision of self-driving storage. Such AI platforms maybe configured to deliver global predictive intelligence by collectingand analyzing large amounts of storage system telemetry data points toenable effortless management, analytics and support. In fact, suchstorage systems may be capable of predicting both capacity andperformance, as well as generating intelligent advice on workloaddeployment, interaction and optimization. Such AI platforms may beconfigured to scan all incoming storage system telemetry data against alibrary of issue fingerprints to predict and resolve incidents inreal-time, before they impact customer environments, and captureshundreds of variables related to performance that are used to forecastperformance load.

The storage systems described above may support the serialized orsimultaneous execution artificial intelligence applications, machinelearning applications, data analytics applications, datatransformations, and other tasks that collectively may form an AIladder. Such an AI ladder may effectively be formed by combining suchelements to form a complete data science pipeline, where existdependencies between elements of the AI ladder. For example, AI mayrequire that some form of machine learning has taken place, machinelearning may require that some form of analytics has taken place,analytics may require that some form of data and informationarchitecting has taken place, and so on. As such, each element may beviewed as a rung in an AI ladder that collectively can form a completeand sophisticated AI solution.

The storage systems described above may also, either alone or incombination with other computing environments, be used to deliver an AIeverywhere experience where AI permeates wide and expansive aspects ofbusiness and life. For example, AI may play an important role in thedelivery of deep learning solutions, deep reinforcement learningsolutions, artificial general intelligence solutions, autonomousvehicles, cognitive computing solutions, commercial UAVs or drones,conversational user interfaces, enterprise taxonomies, ontologymanagement solutions, machine learning solutions, smart dust, smartrobots, smart workplaces, and many others. The storage systems describedabove may also, either alone or in combination with other computingenvironments, be used to deliver a wide range of transparently immersiveexperiences where technology can introduce transparency between people,businesses, and things. Such transparently immersive experiences may bedelivered as augmented reality technologies, connected homes, virtualreality technologies, brain-computer interfaces, human augmentationtechnologies, nanotube electronics, volumetric displays, 4D printingtechnologies, or others. The storage systems described above may also,either alone or in combination with other computing environments, beused to support a wide variety of digital platforms. Such digitalplatforms can include, for example, 5G wireless systems and platforms,digital twin platforms, edge computing platforms, IoT platforms, quantumcomputing platforms, serverless PaaS, software-defined security,neuromorphic computing platforms, and so on.

Readers will appreciate that some transparently immersive experiencesmay involve the use of digital twins of various “things” such as people,places, processes, systems, and so on. Such digital twins and otherimmersive technologies can alter the way that humans interact withtechnology, as conversational platforms, augmented reality, virtualreality and mixed reality provide a more natural and immersiveinteraction with the digital world. In fact, digital twins may be linkedwith the real-world, perhaps even in real-time, to understand the stateof a thing or system, respond to changes, and so on. Because digitaltwins consolidate massive amounts of information on individual assetsand groups of assets (even possibly providing control of those assets),digital twins may communicate with each other to digital factory modelsof multiple linked digital twins.

The storage systems described above may also be part of a multi-cloudenvironment in which multiple cloud computing and storage services aredeployed in a single heterogeneous architecture. In order to facilitatethe operation of such a multi-cloud environment, DevOps tools may bedeployed to enable orchestration across clouds. Likewise, continuousdevelopment and continuous integration tools may be deployed tostandardize processes around continuous integration and delivery, newfeature rollout and provisioning cloud workloads. By standardizing theseprocesses, a multi-cloud strategy may be implemented that enables theutilization of the best provider for each workload. Furthermore,application monitoring and visibility tools may be deployed to moveapplication workloads around different clouds, identify performanceissues, and perform other tasks. In addition, security and compliancetools may be deployed for to ensure compliance with securityrequirements, government regulations, and so on. Such a multi-cloudenvironment may also include tools for application delivery and smartworkload management to ensure efficient application delivery and helpdirect workloads across the distributed and heterogeneousinfrastructure, as well as tools that ease the deployment andmaintenance of packaged and custom applications in the cloud and enableportability amongst clouds. The multi-cloud environment may similarlyinclude tools for data portability.

The storage systems described above may be used as a part of a platformto enable the use of crypto-anchors that may be used to authenticate aproduct's origins and contents to ensure that it matches a blockchainrecord associated with the product. Such crypto-anchors may take manyforms including, for example, as edible ink, as a mobile sensor, as amicrochip, and others. Similarly, as part of a suite of tools to securedata stored on the storage system, the storage systems described abovemay implement various encryption technologies and schemes, includinglattice cryptography. Lattice cryptography can involve constructions ofcryptographic primitives that involve lattices, either in theconstruction itself or in the security proof. Unlike public-key schemessuch as the RSA, Diffie-Hellman or Elliptic-Curve cryptosystems, whichare easily attacked by a quantum computer, some lattice-basedconstructions appear to be resistant to attack by both classical andquantum computers.

A quantum computer is a device that performs quantum computing. Quantumcomputing is computing using quantum-mechanical phenomena, such assuperposition and entanglement. Quantum computers differ fromtraditional computers that are based on transistors, as such traditionalcomputers require that data be encoded into binary digits (bits), eachof which is always in one of two definite states (0 or 1). In contrastto traditional computers, quantum computers use quantum bits, which canbe in superpositions of states. A quantum computer maintains a sequenceof qubits, where a single qubit can represent a one, a zero, or anyquantum superposition of those two qubit states. A pair of qubits can bein any quantum superposition of 4 states, and three qubits in anysuperposition of 8 states. A quantum computer with n qubits cangenerally be in an arbitrary superposition of up to 2{circumflex over( )}n different states simultaneously, whereas a traditional computercan only be in one of these states at any one time. A quantum Turingmachine is a theoretical model of such a computer.

The storage systems described above may also be paired withFPGA-accelerated servers as part of a larger AI or ML infrastructure.Such FPGA-accelerated servers may reside near (e.g., in the same datacenter) the storage systems described above or even incorporated into anappliance that includes one or more storage systems, one or moreFPGA-accelerated servers, networking infrastructure that supportscommunications between the one or more storage systems and the one ormore FPGA-accelerated servers, as well as other hardware and softwarecomponents. Alternatively, FPGA-accelerated servers may reside within acloud computing environment that may be used to perform compute-relatedtasks for AI and ML jobs. Any of the embodiments described above may beused to collectively serve as a FPGA-based AI or ML platform. Readerswill appreciate that, in some embodiments of the FPGA-based AI or MLplatform, the FPGAs that are contained within the FPGA-acceleratedservers may be reconfigured for different types of ML models (e.g.,LSTMs, CNNs, GRUs). The ability to reconfigure the FPGAs that arecontained within the FPGA-accelerated servers may enable theacceleration of a ML or AI application based on the most optimalnumerical precision and memory model being used. Readers will appreciatethat by treating the collection of FPGA-accelerated servers as a pool ofFPGAs, any CPU in the data center may utilize the pool of FPGAs as ashared hardware microservice, rather than limiting a server to dedicatedaccelerators plugged into it.

The FPGA-accelerated servers and the GPU-accelerated servers describedabove may implement a model of computing where, rather than keeping asmall amount of data in a CPU and running a long stream of instructionsover it as occurred in more traditional computing models, the machinelearning model and parameters are pinned into the high-bandwidth on-chipmemory with lots of data streaming though the high-bandwidth on-chipmemory. FPGAs may even be more efficient than GPUs for this computingmodel, as the FPGAs can be programmed with only the instructions neededto run this kind of computing model.

The storage systems described above may be configured to provideparallel storage, for example, through the use of a parallel file systemsuch as BeeGFS. Such parallel files systems may include a distributedmetadata architecture. For example, the parallel file system may includea plurality of metadata servers across which metadata is distributed, aswell as components that include services for clients and storageservers. Through the use of a parallel file system, file contents may bedistributed over a plurality of storage servers using striping andmetadata may be distributed over a plurality of metadata servers on adirectory level, with each server storing a part of the complete filesystem tree. Readers will appreciate that in some embodiments, thestorage servers and metadata servers may run in userspace on top of anexisting local file system. Furthermore, dedicated hardware is notrequired for client services, the metadata servers, or the hardwareservers as metadata servers, storage servers, and even the clientservices may be run on the same machines.

Readers will appreciate that, in part due to the emergence of many ofthe technologies discussed above including mobile devices, cloudservices, social networks, big data analytics, and so on, an informationtechnology platform may be needed to integrate all of these technologiesand drive new business opportunities by quickly deliveringrevenue-generating products, services, and experiences—rather thanmerely providing the technology to automate internal business processes.Information technology organizations may need to balance resources andinvestments needed to keep core legacy systems up and running while alsointegrating technologies to build an information technology platformthat can provide the speed and flexibility in areas such as, forexample, exploiting big data, managing unstructured data, and workingwith cloud applications and services. One possible embodiment of such aninformation technology platform is a composable infrastructure thatincludes fluid resource pools, such as many of the systems describedabove that, can meet the changing needs of applications by allowing forthe composition and recomposition of blocks of disaggregated compute,storage, and fabric infrastructure. Such a composable infrastructure canalso include a single management interface to eliminate complexity and aunified API to discover, search, inventory, configure, provision,update, and diagnose the composable infrastructure.

The systems described above can support the execution of a wide array ofsoftware applications. Such software applications can be deployed in avariety of ways, including container-based deployment models.Containerized applications may be managed using a variety of tools. Forexample, containerized applications may be managed using Docker Swarm, aclustering and scheduling tool for Docker containers that enables ITadministrators and developers to establish and manage a cluster ofDocker nodes as a single virtual system. Likewise, containerizedapplications may be managed through the use of Kubernetes, acontainer-orchestration system for automating deployment, scaling andmanagement of containerized applications. Kubernetes may execute on topof operating systems such as, for example, Red Hat Enterprise Linux,Ubuntu Server, SUSE Linux Enterprise Servers, and others. In suchexamples, a master node may assign tasks to worker/minion nodes.Kubernetes can include a set of components (e.g., kubelet, kube-proxy,cAdvisor) that manage individual nodes as a well as a set of components(e.g., etcd, API server, Scheduler, Control Manager) that form a controlplane. Various controllers (e.g., Replication Controller, DaemonSetController) can drive the state of a Kubernetes cluster by managing aset of pods that includes one or more containers that are deployed on asingle node. Containerized applications may be used to facilitate aserverless, cloud native computing deployment and management model forsoftware applications. In support of a serverless, cloud nativecomputing deployment and management model for software applications,containers may be used as part of an event handling mechanisms (e.g.,AWS Lambdas) such that various events cause a containerized applicationto be spun up to operate as an event handler.

The systems described above may be deployed in a variety of ways,including being deployed in ways that support fifth generation (‘5G’)networks. 5G networks may support substantially faster datacommunications than previous generations of mobile communicationsnetworks and, as a consequence may lead to the disaggregation of dataand computing resources as modern massive data centers may become lessprominent and may be replaced, for example, by more-local, micro datacenters that are close to the mobile-network towers. The systemsdescribed above may be included in such local, micro data centers andmay be part of or paired to multi-access edge computing (‘MEC’) systems.Such MEC systems may enable cloud computing capabilities and an ITservice environment at the edge of the cellular network. By runningapplications and performing related processing tasks closer to thecellular customer, network congestion may be reduced and applicationsmay perform better. MEC technology is designed to be implemented at thecellular base stations or other edge nodes, and enables flexible andrapid deployment of new applications and services for customers. MEC mayalso allow cellular operators to open their radio access network (‘RAN’)to authorized third-parties, such as application developers and contentprovider. Furthermore, edge computing and micro data centers maysubstantially reduce the cost of smartphones that work with the 5Gnetwork because customer may not need devices with such intensiveprocessing power and the expensive requisite components.

Readers will appreciate that 5G networks may generate more data thanprevious network generations, especially in view of the fact that thehigh network bandwidth offered by 5G networks may cause the 5G networksto handle amounts and types of data (e.g., sensor data from self-drivingcars, data generated by AR/VR technologies) that weren't as feasible forprevious generation networks. In such examples, the scalability offeredby the systems described above may be very valuable as the amount ofdata increases, adoption of emerging technologies increase, and so on.

For further explanation, FIG. 3D illustrates an exemplary computingdevice 350 that may be specifically configured to perform one or more ofthe processes described herein. As shown in FIG. 3D, computing device350 may include a communication interface 352, a processor 354, astorage device 356, and an input/output (“I/O”) module 358communicatively connected one to another via a communicationinfrastructure 360. While an exemplary computing device 350 is shown inFIG. 3D, the components illustrated in FIG. 3D are not intended to belimiting. Additional or alternative components may be used in otherembodiments. Components of computing device 350 shown in FIG. 3D willnow be described in additional detail.

Communication interface 352 may be configured to communicate with one ormore computing devices. Examples of communication interface 352 include,without limitation, a wired network interface (such as a networkinterface card), a wireless network interface (such as a wirelessnetwork interface card), a modem, an audio/video connection, and anyother suitable interface.

Processor 354 generally represents any type or form of processing unitcapable of processing data and/or interpreting, executing, and/ordirecting execution of one or more of the instructions, processes,and/or operations described herein. Processor 354 may perform operationsby executing computer-executable instructions 362 (e.g., an application,software, code, and/or other executable data instance) stored in storagedevice 356.

Storage device 356 may include one or more data storage media, devices,or configurations and may employ any type, form, and combination of datastorage media and/or device. For example, storage device 356 mayinclude, but is not limited to, any combination of the non-volatilemedia and/or volatile media described herein. Electronic data, includingdata described herein, may be temporarily and/or permanently stored instorage device 356. For example, data representative ofcomputer-executable instructions 362 configured to direct processor 354to perform any of the operations described herein may be stored withinstorage device 356. In some examples, data may be arranged in one ormore databases residing within storage device 356.

I/O module 358 may include one or more I/O modules configured to receiveuser input and provide user output. I/O module 358 may include anyhardware, firmware, software, or combination thereof supportive of inputand output capabilities. For example, I/O module 358 may includehardware and/or software for capturing user input, including, but notlimited to, a keyboard or keypad, a touchscreen component (e.g.,touchscreen display), a receiver (e.g., an RF or infrared receiver),motion sensors, and/or one or more input buttons.

I/O module 358 may include one or more devices for presenting output toa user, including, but not limited to, a graphics engine, a display(e.g., a display screen), one or more output drivers (e.g., displaydrivers), one or more audio speakers, and one or more audio drivers. Incertain embodiments, I/O module 358 is configured to provide graphicaldata to a display for presentation to a user. The graphical data may berepresentative of one or more graphical user interfaces and/or any othergraphical content as may serve a particular implementation. In someexamples, any of the systems, computing devices, and/or other componentsdescribed herein may be implemented by computing device 350.

For further explanation, FIG. 4 sets forth a block diagram illustratinga plurality of storage systems (402, 404, 406) that support a podaccording to some embodiments of the present disclosure. Althoughdepicted in less detail, the storage systems (402, 404, 406) depicted inFIG. 4 may be similar to the storage systems described above withreference to FIGS. 1A-1D, FIGS. 2A-2G, FIGS. 3A-3B, or any combinationthereof. In fact, the storage systems (402, 404, 406) depicted in FIG. 4may include the same, fewer, or additional components as the storagesystems described above.

In the example depicted in FIG. 4, each of the storage systems (402,404, 406) is depicted as having at least one computer processor (408,410, 412), computer memory (414, 416, 418), and computer storage (420,422, 424). Although in some embodiments the computer memory (414, 416,418) and the computer storage (420, 422, 424) may be part of the samehardware devices, in other embodiments the computer memory (414, 416,418) and the computer storage (420, 422, 424) may be part of differenthardware devices. The distinction between the computer memory (414, 416,418) and the computer storage (420, 422, 424) in this particular examplemay be that the computer memory (414, 416, 418) is physically proximateto the computer processors (408, 410, 412) and may store computerprogram instructions that are executed by the computer processors (408,410, 412), while the computer storage (420, 422, 424) is embodied asnon-volatile storage for storing user data, metadata describing the userdata, and so on. Referring to the example above in FIG. 1A, for example,the computer processors (408, 410, 412) and computer memory (414, 416,418) for a particular storage system (402, 404, 406) may reside withinone of more of the controllers (110A-110D) while the attached storagedevices (171A-171F) may serve as the computer storage (420, 422, 424)within a particular storage system (402, 404, 406).

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may attach to one or more pods (430, 432) according to someembodiments of the present disclosure. Each of the pods (430, 432)depicted in FIG. 4 can include a dataset (426, 428). For example, afirst pod (430) that three storage systems (402, 404, 406) have attachedto includes a first dataset (426) while a second pod (432) that twostorage systems (404, 406) have attached to includes a second dataset(428). In such an example, when a particular storage system attaches toa pod, the pod's dataset is copied to the particular storage system andthen kept up to date as the dataset is modified. Storage systems can beremoved from a pod, resulting in the dataset being no longer kept up todate on the removed storage system. In the example depicted in FIG. 4,any storage system which is active for a pod (it is an up-to-date,operating, non-faulted member of a non-faulted pod) can receive andprocess requests to modify or read the pod's dataset.

In the example depicted in FIG. 4, each pod (430, 432) may also includea set of managed objects and management operations, as well as a set ofaccess operations to modify or read the dataset (426, 428) that isassociated with the particular pod (430, 432). In such an example, themanagement operations may modify or query managed objects equivalentlythrough any of the storage systems. Likewise, access operations to reador modify the dataset may operate equivalently through any of thestorage systems. In such an example, while each storage system stores aseparate copy of the dataset as a proper subset of the datasets storedand advertised for use by the storage system, the operations to modifymanaged objects or the dataset performed and completed through any onestorage system are reflected in subsequent management objects to querythe pod or subsequent access operations to read the dataset.

Readers will appreciate that pods may implement more capabilities thanjust a clustered synchronously replicated dataset. For example, pods canbe used to implement tenants, whereby datasets are in some way securelyisolated from each other. Pods can also be used to implement virtualarrays or virtual storage systems where each pod is presented as aunique storage entity on a network (e.g., a Storage Area Network, orInternet Protocol network) with separate addresses. In the case of amulti-storage-system pod implementing a virtual storage system, allphysical storage systems associated with the pod may present themselvesas in some way the same storage system (e.g., as if the multiplephysical storage systems were no different than multiple network portsinto a single storage system).

Readers will appreciate that pods may also be units of administration,representing a collection of volumes, file systems, object/analyticstores, snapshots, and other administrative entities, where makingadministrative changes (e.g., name changes, property changes, managingexports or permissions for some part of the pod's dataset), on any onestorage system is automatically reflected to all active storage systemsassociated with the pod. In addition, pods could also be units of datacollection and data analysis, where performance and capacity metrics arepresented in ways that aggregate across all active storage systems forthe pod, or that call out data collection and analysis separately foreach pod, or perhaps presenting each attached storage system'scontribution to the incoming content and performance for each a pod.

One model for pod membership may be defined as a list of storagesystems, and a subset of that list where storage systems are consideredto be in-sync for the pod. A storage system may be considered to bein-sync for a pod if it is at least within a recovery of havingidentical idle content for the last written copy of the datasetassociated with the pod. Idle content is the content after anyin-progress modifications have completed with no processing of newmodifications. Sometimes this is referred to as “crash recoverable”consistency. Recovery of a pod carries out the process of reconcilingdifferences in applying concurrent updates to in-sync storage systems inthe pod. Recovery can resolve any inconsistencies between storagesystems in the completion of concurrent modifications that had beenrequested to various members of the pod but that were not signaled toany requestor as having completed successfully. Storage systems that arelisted as pod members but that are not listed as in-sync for the pod canbe described as “detached” from the pod. Storage systems that are listedas pod members, are in-sync for the pod, and are currently available foractively serving data for the pod are “online” for the pod.

Each storage system member of a pod may have its own copy of themembership, including which storage systems it last knew were in-sync,and which storage systems it last knew comprised the entire set of podmembers. To be online for a pod, a storage system must consider itselfto be in-sync for the pod and must be communicating with all otherstorage systems it considers to be in-sync for the pod. If a storagesystem can't be certain that it is in-sync and communicating with allother storage systems that are in-sync, then it must stop processing newincoming requests for the pod (or must complete them with an error orexception) until it can be certain that it is in-sync and communicatingwith all other storage systems that are in-sync. A first storage systemmay conclude that a second paired storage system should be detached,which will allow the first storage system to continue since it is nowin-sync with all storage systems now in the list. But, the secondstorage system must be prevented from concluding, alternatively, thatthe first storage system should be detached and with the second storagesystem continuing operation. This would result in a “split brain”condition that can lead to irreconcilable datasets, dataset corruption,or application corruption, among other dangers.

The situation of needing to determine how to proceed when notcommunicating with paired storage systems can arise while a storagesystem is running normally and then notices lost communications, whileit is currently recovering from some previous fault, while it isrebooting or resuming from a temporary power loss or recoveredcommunication outage, while it is switching operations from one set ofstorage system controller to another set for whatever reason, or duringor after any combination of these or other kinds of events. In fact, anytime a storage system that is associated with a pod can't communicatewith all known non-detached members, the storage system can either waitbriefly until communications can be established, go offline and continuewaiting, or it can determine through some means that it is safe todetach the non-communicating storage system without risk of incurring asplit brain due to the non-communicating storage system concluding thealternative view, and then continue. If a safe detach can happen quicklyenough, the storage system can remain online for the pod with littlemore than a short delay and with no resulting application outages forapplications that can issue requests to the remaining online storagesystems.

One example of this situation is when a storage system may know that itis out-of-date. That can happen, for example, when a first storagesystem is first added to a pod that is already associated with one ormore storage systems, or when a first storage system reconnects toanother storage system and finds that the other storage system hadalready marked the first storage system as detached. In this case, thisfirst storage system will simply wait until it connects to some otherset of storage systems that are in-sync for the pod.

This model demands some degree of consideration for how storage systemsare added to or removed from pods or from the in-sync pod members list.Since each storage system will have its own copy of the list, and sincetwo independent storage systems can't update their local copy at exactlythe same time, and since the local copy is all that is available on areboot or in various fault scenarios, care must be taken to ensure thattransient inconsistencies don't cause problems. For example, if onestorage systems is in-sync for a pod and a second storage system isadded, then if the second storage system is updated to list both storagesystems as in-sync first, then if there is a fault and a restart of bothstorage systems, the second might startup and wait to connect to thefirst storage system while the first might be unaware that it should orcould wait for the second storage system. If the second storage systemthen responds to an inability to connect with the first storage systemby going through a process to detach it, then it might succeed incompleting a process that the first storage system is unaware of,resulting in a split brain. As such, it may be necessary to ensure thatstorage systems won't disagree inappropriately on whether they might optto go through a detach process if they aren't communicating.

One way to ensure that storage systems won't disagree inappropriately onwhether they might opt to go through a detach process if they aren'tcommunicating is to ensure that when adding a new storage system to thein-sync member list for a pod, the new storage system first stores thatit is a detached member (and perhaps that it is being added as anin-sync member). Then, the existing in-sync storage systems can locallystore that the new storage system is an in-sync pod member before thenew storage system locally stores that same fact. If there is a set ofreboots or network outages prior to the new storage system storing itsin-sync status, then the original storage systems may detach the newstorage system due to non-communication, but the new storage system willwait. A reverse version of this change might be needed for removing acommunicating storage system from a pod: first the storage system beingremoved stores that it is no longer in-sync, then the storage systemsthat will remain store that the storage system being removed is nolonger in-sync, then all storage systems delete the storage system beingremoved from their pod membership lists. Depending on theimplementation, an intermediate persisted detached state may not benecessary. Whether or not care is required in local copies of membershiplists may depend on the model storage systems use for monitoring eachother or for validating their membership. If a consensus model is usedfor both, or if an external system (or an external distributed orclustered system) is used to store and validate pod membership, theninconsistencies in locally stored membership lists may not matter.

When communications fail or one or several storage systems in a podfail, or when a storage system starts up (or fails over to a secondarycontroller) and can't communicate with paired storage systems for a pod,and it is time for one or more storage systems to decide to detach oneor more paired storage systems, some algorithm or mechanism must beemployed to decide that it is safe to do so and to follow through on thedetach. One means of resolving detaches is use a majority (or quorum)model for membership. With three storage systems, as long as two arecommunicating, they can agree to detach a third storage system thatisn't communicating, but that third storage system cannot by itselfchoose to detach either of the other two. Confusion can arise whenstorage system communication is inconsistent. For example, storagesystem A might be communicating with storage system B but not C, whilestorage system B might be communicating with both A and C. So, A and Bcould detach C, or B and C could detach A, but more communicationbetween pod members may be needed to figure this out.

Care needs to be taken in a quorum membership model when adding andremoving storage systems. For example, if a fourth storage system isadded, then a “majority” of storage systems is at that point three. Thetransition from three storage systems (with two required for majority)to a pod including a fourth storage system (with three required formajority) may require something similar to the model describedpreviously for carefully adding a storage system to the in-sync list.For example, the fourth storage system might start in an attaching statebut not yet attached where it would never instigate a vote over quorum.Once in that state, the original three pod members could each be updatedto be aware of the fourth member and the new requirement for a threestorage system majority to detach a fourth. Removing a storage systemfrom a pod might similarly move that storage system to a locally stored“detaching” state before updating other pod members. A variant schemefor this is to use a distributed consensus mechanism such as PAXOS orRAFT to implement any membership changes or to process detach requests.

Another means of managing membership transitions is to use an externalsystem that is outside of the storage systems themselves to handle podmembership. In order to become online for a pod, a storage system mustfirst contact the external pod membership system to verify that it isin-sync for the pod. Any storage system that is online for a pod shouldthen remain in communication with the pod membership system and shouldwait or go offline if it loses communication. An external pod membershipmanager could be implemented as a highly available cluster using variouscluster tools, such as Oracle RAC, Linux HA, VERITAS Cluster Server,IBM's HACMP, or others. An external pod membership manager could alsouse distributed configuration tools such as Etcd or Zookeeper, or areliable distributed database such as Amazon's DynamoDB.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may receive a request to read a portion of the dataset (426,428) and process the request to read the portion of the dataset locallyaccording to some embodiments of the present disclosure. Readers willappreciate that although requests to modify (e.g., a write operation)the dataset (426, 428) require coordination between the storage systems(402, 404, 406) in a pod, as the dataset (426, 428) should be consistentacross all storage systems (402, 404, 406) in a pod, responding to arequest to read a portion of the dataset (426, 428) does not requiresimilar coordination between the storage systems (402, 404, 406). Assuch, a particular storage system that receives a read request mayservice the read request locally by reading a portion of the dataset(426, 428) that is stored within the storage system's storage devices,with no synchronous communication with other storage systems in the pod.Read requests received by one storage system for a replicated dataset ina replicated cluster are expected to avoid any communication in the vastmajority of cases, at least when received by a storage system that isrunning within a cluster that is also running nominally. Such readsshould normally be processed simply by reading from the local copy of aclustered dataset with no further interaction required with otherstorage systems in the cluster

Readers will appreciate that the storage systems may take steps toensure read consistency such that a read request will return the sameresult regardless of which storage system processes the read request.For example, the resulting clustered dataset content for any set ofupdates received by any set of storage systems in the cluster should beconsistent across the cluster, at least at any time updates are idle(all previous modifying operations have been indicated as complete andno new update requests have been received and processed in any way).More specifically, the instances of a clustered dataset across a set ofstorage systems can differ only as a result of updates that have not yetcompleted. This means, for example, that any two write requests whichoverlap in their volume block range, or any combination of a writerequest and an overlapping snapshot, compare-and-write, or virtual blockrange copy, must yield a consistent result on all copies of the dataset.Two operations should not yield a result as if they happened in oneorder on one storage system and a different order on another storagesystem in the replicated cluster.

Furthermore, read requests can be made time order consistent. Forexample, if one read request is received on a replicated cluster andcompleted and that read is then followed by another read request to anoverlapping address range which is received by the replicated clusterand where one or both reads in any way overlap in time and volumeaddress range with a modification request received by the replicatedcluster (whether any of the reads or the modification are received bythe same storage system or a different storage system in the replicatedcluster), then if the first read reflects the result of the update thenthe second read should also reflect the results of that update, ratherthan possibly returning data that preceded the update. If the first readdoes not reflect the update, then the second read can either reflect theupdate or not. This ensures that between two read requests “time” for adata segment cannot roll backward.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may also detect a disruption in data communications with oneor more of the other storage systems and determine whether to theparticular storage system should remain in the pod. A disruption in datacommunications with one or more of the other storage systems may occurfor a variety of reasons. For example, a disruption in datacommunications with one or more of the other storage systems may occurbecause one of the storage systems has failed, because a networkinterconnect has failed, or for some other reason. An important aspectof synchronous replicated clustering is ensuring that any fault handlingdoesn't result in unrecoverable inconsistencies, or any inconsistency inresponses. For example, if a network fails between two storage systems,at most one of the storage systems can continue processing newlyincoming I/O requests for a pod. And, if one storage system continuesprocessing, the other storage system can't process any new requests tocompletion, including read requests.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may also determine whether the particular storage systemshould remain in the pod in response to detecting a disruption in datacommunications with one or more of the other storage systems. Asmentioned above, to be ‘online’ as part of a pod, a storage system mustconsider itself to be in-sync for the pod and must be communicating withall other storage systems it considers to be in-sync for the pod. If astorage system can't be certain that it is in-sync and communicatingwith all other storage systems that are in-sync, then it may stopprocessing new incoming requests to access the dataset (426, 428). Assuch, the storage system may determine whether to the particular storagesystem should remain online as part of the pod, for example, bydetermining whether it can communicate with all other storage systems itconsiders to be in-sync for the pod (e.g., via one or more testmessages), by determining whether the all other storage systems itconsiders to be in-sync for the pod also consider the storage system tobe attached to the pod, through a combination of both steps where theparticular storage system must confirm that it can communicate with allother storage systems it considers to be in-sync for the pod and thatall other storage systems it considers to be in-sync for the pod alsoconsider the storage system to be attached to the pod, or through someother mechanism.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may also keep the dataset on the particular storage systemaccessible for management and dataset operations in response todetermining that the particular storage system should remain in the pod.The storage system may keep the dataset (426, 428) on the particularstorage system accessible for management and dataset operations, forexample, by accepting requests to access the version of the dataset(426, 428) that is stored on the storage system and processing suchrequests, by accepting and processing management operations associatedwith the dataset (426, 428) that are issued by a host or authorizedadministrator, by accepting and processing management operationsassociated with the dataset (426, 428) that are issued by one of theother storage systems, or in some other way.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may, however, make the dataset on the particular storagesystem inaccessible for management and dataset operations in response todetermining that the particular storage system should not remain in thepod. The storage system may make the dataset (426, 428) on theparticular storage system inaccessible for management and datasetoperations, for example, by rejecting requests to access the version ofthe dataset (426, 428) that is stored on the storage system, byrejecting management operations associated with the dataset (426, 428)that are issued by a host or other authorized administrator, byrejecting management operations associated with the dataset (426, 428)that are issued by one of the other storage systems in the pod, or insome other way.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may also detect that the disruption in data communicationswith one or more of the other storage systems has been repaired and makethe dataset on the particular storage system accessible for managementand dataset operations. The storage system may detect that thedisruption in data communications with one or more of the other storagesystems has been repaired, for example, by receiving a message from theone or more of the other storage systems. In response to detecting thatthe disruption in data communications with one or more of the otherstorage systems has been repaired, the storage system may make thedataset (426, 428) on the particular storage system accessible formanagement and dataset operations once the previously detached storagesystem has been resynchronized with the storage systems that remainedattached to the pod.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may also go offline from the pod such that the particularstorage system no longer allows management and dataset operations. Thedepicted storage systems (402, 404, 406) may go offline from the podsuch that the particular storage system no longer allows management anddataset operations for a variety of reasons. For example, the depictedstorage systems (402, 404, 406) may also go offline from the pod due tosome fault with the storage system itself, because an update or someother maintenance is occurring on the storage system, due tocommunications faults, or for many other reasons. In such an example,the depicted storage systems (402, 404, 406) may subsequently update thedataset on the particular storage system to include all updates to thedataset since the particular storage system went offline and go backonline with the pod such that the particular storage system allowsmanagement and dataset operations, as will be described in greaterdetail in the resynchronization sections included below.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may also identifying a target storage system forasynchronously receiving the dataset, where the target storage system isnot one of the plurality of storage systems across which the dataset issynchronously replicated. Such a target storage system may represent,for example, a backup storage system, as some storage system that makesuse of the synchronously replicated dataset, and so on. In fact,synchronous replication can be leveraged to distribute copies of adataset closer to some rack of servers, for better local readperformance. One such case is smaller top-of-rack storage systemssymmetrically replicated to larger storage systems that are centrallylocated in the data center or campus and where those larger storagesystems are more carefully managed for reliability or are connected toexternal networks for asynchronous replication or backup services.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may also identify a portion of the dataset that is not beingasynchronously replicated to the target storage system by any of theother storages systems and asynchronously replicate, to the targetstorage system, the portion of the dataset that is not beingasynchronously replicated to the target storage system by any of theother storages systems, wherein the two or more storage systemscollectively replicate the entire dataset to the target storage system.In such a way, the work associated with asynchronously replicating aparticular dataset may be split amongst the members of a pod, such thateach storage system in a pod is only responsible for asynchronouslyreplicating a subset of a dataset to the target storage system.

In the example depicted in FIG. 4, the depicted storage systems (402,404, 406) may also detach from the pod, such that the particular storagesystem that detaches from the pod is no longer included in the set ofstorage systems across which the dataset is synchronously replicated.For example, if storage system (404) in FIG. 4 detached from the pod(430) illustrated in FIG. 4, the pod (430) would only include storagesystems (402, 406) as the storage systems across which the dataset (426)that is included in the pod (430) would be synchronously replicatedacross. In such an example, detaching the storage system from the podcould also include removing the dataset from the particular storagesystem that detached from the pod. Continuing with the example where thestorage system (404) in FIG. 4 detached from the pod (430) illustratedin FIG. 4, the dataset (426) that is included in the pod (430) could bedeleted or otherwise removed from the storage system (404).

Readers will appreciate that there are a number of unique administrativecapabilities enabled by the pod model that can further be supported.Also, the pod model itself introduces some issues that can be addressedby an implementation. For example, when a storage system is offline fora pod, but is otherwise running, such as because an interconnect failedand another storage system for the pod won out in mediation, there maystill be a desire or need to access the offline pod's dataset on theoffline storage system. One solution may be simply to enable the pod insome detached mode and allow the dataset to be accessed. However, thatsolution can be dangerous and that solution can cause the pod's metadataand data to be much more difficult to reconcile when the storage systemsdo regain communication. Furthermore, there could still be a separatepath for hosts to access the offline storage system as well as the stillonline storage systems. In that case, a host might issue I/O to bothstorage systems even though they are no longer being kept in sync,because the host sees target ports reporting volumes with the sameidentifiers and the host I/O drivers presume it sees additional paths tothe same volume. This can result in fairly damaging data corruption asreads and writes issued to both storage systems are no longer consistenteven though the host presumes they are. As a variant of this case, in aclustered application, such as a shared storage clustered database, theclustered application running on one host might be reading or writing toone storage system and the same clustered application running on anotherhost might be reading or writing to the “detached” storage system, yetthe two instances of the clustered application are communicating betweeneach other on the presumption that the dataset they each see is entirelyconsistent for completed writes. Since they aren't consistent, thatpresumption is violated and the application's dataset (e.g., thedatabase) can quickly end up being corrupted.

One way to solve both of these problems is to allow for an offline pod,or perhaps a snapshot of an offline pod, to be copied to a new pod withnew volumes that have sufficiently new identities that host I/O driversand clustered applications won't confuse the copied volumes as being thesame as the still online volumes on another storage system. Since eachpod maintains a complete copy of the dataset, which is crash consistentbut perhaps slightly different from the copy of the pod dataset onanother storage system, and since each pod has an independent copy ofall data and metadata needed to operate on the pod content, it is astraightforward problem to make a virtual copy of some or all volumes orsnapshots in the pod to new volumes in a new pod. In a logical extentgraph implementation, for example, all that is needed is to define newvolumes in a new pod which reference logical extent graphs from thecopied pod associated with the pod's volumes or snapshots, and with thelogical extent graphs being marked as copy on write. The new volumesshould be treated as new volumes, similarly to how volume snapshotscopied to a new volume might be implemented. Volumes may have the sameadministrative name, though within a new pod namespace. But, they shouldhave different underlying identifiers, and differing logical unitidentifiers from the original volumes.

In some cases it may be possible to use virtual network isolationtechniques (for example, by creating a virtual LAN in the case of IPnetworks or a virtual SAN in the case of fiber channel networks) in sucha way that isolation of volumes presented to some interfaces can beassured to be inaccessible from host network interfaces or host SCSIinitiator ports that might also see the original volumes. In such cases,it may be safe to provide the copies of volumes with the same SCSI orother storage identifiers as the original volumes. This could be used,for example, in cases where the applications expect to see a particularset of storage identifiers in order to function without an undue burdenin reconfiguration.

Some of the techniques described herein could also be used outside of anactive fault context to test readiness for handling faults. Readinesstesting (sometimes referred to as “fire drills”) is commonly requiredfor disaster recovery configurations, where frequent and repeatedtesting is considered a necessity to ensure that most or all aspects ofa disaster recovery plan are correct and account for any recent changesto applications, datasets, or changes in equipment. Readiness testingshould be non-disruptive to current production operations, includingreplication. In many cases the real operations can't actually be invokedon the active configuration, but a good way to get close is to usestorage operations to make copies of production datasets, and thenperhaps couple that with the use of virtual networking, to create anisolated environment containing all data that is believed necessary forthe important applications that must be brought up successfully in casesof disasters. Making such a copy of a synchronously replicated (or evenan asynchronously replicated) dataset available within a site (orcollection of sites) that is expected to perform a disaster recoveryreadiness test procedure and then starting the important applications onthat dataset to ensure that it can startup and function is a great tool,since it helps ensure that no important parts of the applicationdatasets were left out in the disaster recovery plan. If necessary, andpractical, this could be coupled with virtual isolated networks coupledperhaps with isolated collection of physical or virtual machines, to getas close as possible to a real world disaster recovery takeoverscenario. Virtually copying a pod (or set of pods) to another pod as apoint-in-time image of the pod datasets immediately creates an isolateddataset that contains all the copied elements and that can then beoperated on essentially identically to the originally pods, as well asallowing isolation to a single site (or a few sites) separately from theoriginal pod. Further, these are fast operations and they can be torndown and repeated easily allowing testing to repeated as often as isdesired.

Some enhancements could be made to get further toward perfect disasterrecovery testing. For example, in conjunction with isolated networks,SCSI logical unit identities or other types of identities could becopied into the target pod so that the test servers, virtual machines,and applications see the same identities. Further, the administrativeenvironment of the servers could be configured to respond to requestsfrom a particular virtual set of virtual networks to respond to requestsand operations on the original pod name so scripts don't require use oftest-variants with alternate “test” versions of object names. A furtherenhancement can be used in cases where the host-side serverinfrastructure that will take over in the case of a disaster takeovercan be used during a test. This includes cases where a disaster recoverydata center is completely stocked with alternative server infrastructurethat won't generally be used until directed to do so by a disaster. Italso includes cases where that infrastructure might be used fornon-critical operations (for example, running analytics on productiondata, or simply supporting application development or other functionswhich may be important but can be halted if needed for more criticalfunctions). Specifically, host definitions and configurations and theserver infrastructure that will use them can be set up as they will befor an actual disaster recovery takeover event and tested as part ofdisaster recovery takeover testing, with the tested volumes beingconnected to these host definitions from the virtual pod copy used toprovide a snapshot of the dataset. From the standpoint of the storagesystems involved, then, these host definitions and configurations usedfor testing, and the volume-to-host connection configurations usedduring testing, can be reused when an actual disaster takeover event istriggered, greatly minimizing the configuration differences between thetest configuration and the real configuration that will be used in caseof a disaster recovery takeover.

In some cases it may make sense to move volumes out of a first pod andinto a new second pod including just those volumes. The pod membershipand high availability and recovery characteristics can then be adjustedseparately, and administration of the two resulting pod datasets canthen be isolated from each other. An operation that can be done in onedirection should also be possible in the other direction. At some point,it may make sense to take two pods and merge them into one so that thevolumes in each of the original two pods will now track each other forstorage system membership and high availability and recoverycharacteristics and events. Both operations can be accomplished safelyand with reasonably minimal or no disruption to running applications byrelying on the characteristics suggested for changing mediation orquorum properties for a pod which were discussed in an earlier section.With mediation, for example, a mediator for a pod can be changed using asequence consisting of a step where each storage system in a pod ischanged to depend on both a first mediator and a second mediator andeach is then changed to depend only on the second mediator. If a faultoccurs in the middle of the sequence, some storage systems may depend onboth the first mediator and the second mediator, but in no case willrecovery and fault handling result in some storage systems dependingonly on the first mediator and other storage systems only depending onthe second mediator. Quorum can be handled similarly by temporarilydepending on winning against both a first quorum model and a secondquorum model in order to proceed to recovery. This may result in a veryshort time period where availability of the pod in the face of faultsdepend on additional resources, thus reducing potential availability,but this time period is very short and the reduction in availability isoften very little. With mediation, if the change in mediator parametersis nothing more than the change in the key used for mediation and themediation service used is the same, then the potential reduction inavailability is even less, since it now depends only on two calls to thesame service versus one call to that service, and rather than separatecalls to two separate services.

Readers will note that changing the quorum model may be quite complex.An additional step may be necessary where storage systems willparticipate in the second quorum model but won't depend on winning inthat second quorum model, which is then followed by the step of alsodepending on the second quorum model. This may be necessary to accountfor the fact that if only one system has processed the change to dependon the quorum model, then it will never win quorum since there willnever be a majority. With this model in place for changing the highavailability parameters (mediation relationship, quorum model, takeoverpreferences), we can create a safe procedure for these operations tosplit a pod into two or to join two pods into one. This may requireadding one other capability: linking a second pod to a first pod forhigh availability such that if two pods include compatible highavailability parameters the second pod linked to the first pod candepend on the first pod for determining and instigating detach-relatedprocessing and operations, offline and in-sync states, and recovery andresynchronization actions.

To split a pod into two, which is an operation to move some volumes intoa newly created pod, a distributed operation may be formed that can bedescribed as: form a second pod into which we will move a set of volumeswhich were previously in a first pod, copy the high availabilityparameters from the first pod into the second pod to ensure they arecompatible for linking, and link the second pod to the first pod forhigh availability. This operation may be encoded as messages and shouldbe implemented by each storage system in the pod in such a way that thestorage system ensures that the operation happens completely on thatstorage system or does not happen at all if processing is interrupted bya fault. Once all in-sync storage systems for the two pods haveprocessed this operation, the storage systems can then process asubsequent operation which changes the second pod so that it is nolonger linked to the first pod. As with other changes to highavailability characteristics for a pod, this involves first having eachin-sync storage system change to rely on both the previous model (thatmodel being that high availability is linked to the first pod) and thenew model (that model being its own now independent high availability).In the case of mediation or quorum, this means that storage systemswhich processed this change will first depend on mediation or quorumbeing achieved as appropriate for the first pod and will additionallydepend on a new separate mediation (for example, a new mediation key) orquorum being achieved for the second pod before the second pod canproceed following a fault that required mediation or testing for quorum.As with the previous description of changing quorum models, anintermediate step may set storage systems to participate in quorum forthe second pod before the step where storage systems participate in anddepend on quorum for the second pod. Once all in-sync storage systemshave processed the change to depend on the new parameters for mediationor quorum for both the first pod and the second pod, the split iscomplete.

Joining a second pod into a first pod operates essentially in reverse.First, the second pod must be adjusted to be compatible with the firstpod, by having an identical list of storage systems and by having acompatible high availability model. This may involve some set of stepssuch as those described elsewhere in this paper to add or remove storagesystems or to change mediator and quorum models. Depending onimplementation, it may be necessary only to reach an identical list ofstorage systems. Joining proceeds by processing an operation on eachin-sync storage system to link the second pod to the first pod for highavailability. Each storage system which processes that operation willthen depend on the first pod for high availability and then the secondpod for high availability. Once all in-sync storage systems for thesecond pod have processed that operation, the storage systems will theneach process a subsequent operation to eliminate the link between thesecond pod and the first pod, migrate the volumes from the second podinto the first pod, and delete the second pod. Host or applicationdataset access can be preserved throughout these operations, as long asthe implementation allows proper direction of host or applicationdataset modification or read operations to the volume by identity and aslong as the identity is preserved as appropriate to the storage protocolor storage model (for example, as long as logical unit identifiers forvolumes and use of target ports for accessing volumes are preserved inthe case of SCSI).

Migrating a volume between pods may present issues. If the pods have anidentical set of in-sync membership storage systems, then it may bestraightforward: temporarily suspend operations on the volumes beingmigrated, switch control over operations on those volumes to controllingsoftware and structures for the new pod, and then resume operations.This allows for a seamless migration with continuous uptime forapplications apart from the very brief operation suspension, providednetwork and ports migrate properly between pods. Depending on theimplementation, suspending operations may not even be necessary, or maybe so internal to the system that the suspension of operations has noimpact. Copying volumes between pods with different in-sync membershipsets is more of a problem. If the target pod for the copy has a subsetof in-sync members from the source pod, this isn't much of a problem: amember storage system can be dropped safely enough without having to domore work. But, if the target pod adds in-sync member storage systems tothe volume over the source pod, then the added storage systems must besynchronized to include the volume's content before they can be used.Until synchronized, this leaves the copied volumes distinctly differentfrom the already synchronized volumes, in that fault handling differsand request handling from the not yet synced member storage systemseither won't work or must be forwarded or won't be as fast because readswill have to traverse an interconnect. Also, the internal implementationwill have to handle some volumes being in sync and ready for faulthandling and others not being in sync.

There are other problems relating to reliability of the operation in theface of faults. Coordinating a migration of volumes betweenmulti-storage-system pods is a distributed operation. If pods are theunit of fault handling and recovery, and if mediation or quorum orwhatever means are used to avoid split-brain situations, then a switchin volumes from one pod with a particular set of state andconfigurations and relationships for fault handling, recovery, mediationand quorum to another then storage systems in a pod have to be carefulabout coordinating changes related to that handling for any volumes.Operations can't be atomically distributed between storage systems, butmust be staged in some way. Mediation and quorum models essentiallyprovide pods with the tools for implementing distributed transactionalatomicity, but this may not extend to inter-pod operations withoutadding to the implementation.

Consider even a simple migration of a volume from a first pod to asecond pod even for two pods that share the same first and secondstorage systems. At some point the storage systems will coordinate todefine that the volume is now in the second pod and is no longer in thefirst pod. If there is no inherent mechanism for transactional atomicityacross the storage systems for the two pods, then a naive implementationcould leave the volume in the first pod on the first storage system andthe second pod on the second storage system at the time of a networkfault that results in fault handling to detach storage systems from thetwo pods. If pods separately determine which storage system succeeds indetaching the other, then the result could be that the same storagesystem detaches the other storage system for both pods, in which casethe result of the volume migration recovery should be consistent, or itcould result in a different storage system detaching the other for thetwo pods. If the first storage system detaches the second storage systemfor the first pod and the second storage system detaches the firststorage system for the second pod, then recovery might result in thevolume being recovered to the first pod on the first storage system andinto the second pod on the second storage system, with the volume thenrunning and exported to hosts and storage applications on both storagesystems. If instead the second storage system detaches the first storagesystem for the first pod and first storage detaches the second storagesystem for the second pod, then recovery might result in the volumebeing discarded from the second pod by the first storage system and thevolume being discarded from the first pod by the second storage system,resulting in the volume disappearing entirely. If the pods a volume isbeing migrated between are on differing sets of storage systems, thenthings can get even more complicated.

A solution to these problems may be to use an intermediate pod alongwith the techniques described previously for splitting and joining pods.This intermediate pod may never be presented as visible managed objectsassociated with the storage systems. In this model, volumes to be movedfrom a first pod to a second pod are first split from the first pod intoa new intermediate pod using the split operation described previously.The storage system members for the intermediate pod can then be adjustedto match the membership of storage systems by adding or removing storagesystems from the pod as necessary. Subsequently, the intermediate podcan be joined with the second pod.

For further explanation, FIG. 5 sets forth a flow chart illustratingsteps that may be performed by storage systems (402, 404, 406) thatsupport a pod according to some embodiments of the present disclosure.Although depicted in less detail, the storage systems (402, 404, 406)depicted in FIG. 5 may be similar to the storage systems described abovewith reference to FIGS. 1A-1D, FIGS. 2A-2G, FIGS. 3A-3B, FIG. 4, or anycombination thereof. In fact, the storage systems (402, 404, 406)depicted in FIG. 5 may include the same, fewer, additional components asthe storage systems described above.

In the example method depicted in FIG. 5, a storage system (402) mayattach (508) to a pod. The model for pod membership may include a listof storage systems and a subset of that list where storage systems arepresumed to be in-sync for the pod. A storage system is in-sync for apod if it is at least within a recovery of having identical idle contentfor the last written copy of the dataset associated with the pod. Idlecontent is the content after any in-progress modifications havecompleted with no processing of new modifications. Sometimes this isreferred to as “crash recoverable” consistency. Storage systems that arelisted as pod members but that are not listed as in-sync for the pod canbe described as “detached” from the pod. Storage systems that are listedas pod members, are in-sync for the pod, and are currently available foractively serving data for the pod are “online” for the pod.

In the example method depicted in FIG. 5, the storage system (402) mayattach (508) to a pod, for example, by synchronizing its locally storedversion of the dataset (426) along with an up-to-date version of thedataset (426) that is stored on other storage systems (404, 406) in thepod that are online, as the term is described above. In such an example,in order for the storage system (402) to attach (508) to the pod, a poddefinition stored locally within each of the storage systems (402, 404,406) in the pod may need to be updated in order for the storage system(402) to attach (508) to the pod. In such an example, each storagesystem member of a pod may have its own copy of the membership,including which storage systems it last knew were in-sync, and whichstorage systems it last knew comprised the entire set of pod members.

In the example method depicted in FIG. 5, the storage system (402) mayalso receive (510) a request to read a portion of the dataset (426) andthe storage system (402) may process (512) the request to read theportion of the dataset (426) locally. Readers will appreciate thatalthough requests to modify (e.g., a write operation) the dataset (426)require coordination between the storage systems (402, 404, 406) in apod, as the dataset (426) should be consistent across all storagesystems (402, 404, 406) in a pod, responding to a request to read aportion of the dataset (426) does not require similar coordinationbetween the storage systems (402, 404, 406). As such, a particularstorage system (402) that receives a read request may service the readrequest locally by reading a portion of the dataset (426) that is storedwithin the storage system's (402) storage devices, with no synchronouscommunication with other storage systems (404, 406) in the pod. Readrequests received by one storage system for a replicated dataset in areplicated cluster are expected to avoid any communication in the vastmajority of cases, at least when received by a storage system that isrunning within a cluster that is also running nominally. Such readsshould normally be processed simply by reading from the local copy of aclustered dataset with no further interaction required with otherstorage systems in the cluster

Readers will appreciate that the storage systems may take steps toensure read consistency such that a read request will return the sameresult regardless of which storage system processes the read request.For example, the resulting clustered dataset content for any set ofupdates received by any set of storage systems in the cluster should beconsistent across the cluster, at least at any time updates are idle(all previous modifying operations have been indicated as complete andno new update requests have been received and processed in any way).More specifically, the instances of a clustered dataset across a set ofstorage systems can differ only as a result of updates that have not yetcompleted. This means, for example, that any two write requests whichoverlap in their volume block range, or any combination of a writerequest and an overlapping snapshot, compare-and-write, or virtual blockrange copy, must yield a consistent result on all copies of the dataset.Two operations cannot yield a result as if they happened in one order onone storage system and a different order on another storage system inthe replicated cluster.

Furthermore, read requests may be time order consistent. For example, ifone read request is received on a replicated cluster and completed andthat read is then followed by another read request to an overlappingaddress range which is received by the replicated cluster and where oneor both reads in any way overlap in time and volume address range with amodification request received by the replicated cluster (whether any ofthe reads or the modification are received by the same storage system ora different storage system in the replicated cluster), then if the firstread reflects the result of the update then the second read should alsoreflect the results of that update, rather than possibly returning datathat preceded the update. If the first read does not reflect the update,then the second read can either reflect the update or not. This ensuresthat between two read requests “time” for a data segment cannot rollbackward.

In the example method depicted in FIG. 5, the storage system (402) mayalso detect (514) a disruption in data communications with one or moreof the other storage systems (404, 406). A disruption in datacommunications with one or more of the other storage systems (404, 406)may occur for a variety of reasons. For example, a disruption in datacommunications with one or more of the other storage systems (404, 406)may occur because one of the storage systems (402, 404, 406) has failed,because a network interconnect has failed, or for some other reason. Animportant aspect of synchronous replicated clustering is ensuring thatany fault handling doesn't result in unrecoverable inconsistencies, orany inconsistency in responses. For example, if a network fails betweentwo storage systems, at most one of the storage systems can continueprocessing newly incoming I/O requests for a pod. And, if one storagesystem continues processing, the other storage system can't process anynew requests to completion, including read requests.

In the example method depicted in FIG. 5, the storage system (402) mayalso determine (516) whether to the particular storage system (402)should remain online as part of the pod. As mentioned above, to be‘online’ as part of a pod, a storage system must consider itself to bein-sync for the pod and must be communicating with all other storagesystems it considers to be in-sync for the pod. If a storage systemcan't be certain that it is in-sync and communicating with all otherstorage systems that are in-sync, then it may stop processing newincoming requests to access the dataset (426). As such, the storagesystem (402) may determine (516) whether to the particular storagesystem (402) should remain online as part of the pod, for example, bydetermining whether it can communicate with all other storage systems(404, 406) it considers to be in-sync for the pod (e.g., via one or moretest messages), by determining whether the all other storage systems(404, 406) it considers to be in-sync for the pod also consider thestorage system (402) to be attached to the pod, through a combination ofboth steps where the particular storage system (402) must confirm thatit can communicate with all other storage systems (404, 406) itconsiders to be in-sync for the pod and that all other storage systems(404, 406) it considers to be in-sync for the pod also consider thestorage system (402) to be attached to the pod, or through some othermechanism.

In the example method depicted in FIG. 5, the storage system (402) mayalso, responsive to affirmatively (518) determining that the particularstorage system (402) should remain online as part of the pod, keep (522)the dataset (426) on the particular storage system (402) accessible formanagement and dataset operations. The storage system (402) may keep(522) the dataset (426) on the particular storage system (402)accessible for management and dataset operations, for example, byaccepting requests to access the version of the dataset (426) that isstored on the storage system (402) and processing such requests, byaccepting and processing management operations associated with thedataset (426) that are issued by a host or authorized administrator, byaccepting and processing management operations associated with thedataset (426) that are issued by one of the other storage systems (404,406) in the pod, or in some other way.

In the example method depicted in FIG. 5, the storage system (402) mayalso, responsive to determining that the particular storage systemshould not (520) remain online as part of the pod, make (524) thedataset (426) on the particular storage system (402) inaccessible formanagement and dataset operations. The storage system (402) may make(524) the dataset (426) on the particular storage system (402)inaccessible for management and dataset operations, for example, byrejecting requests to access the version of the dataset (426) that isstored on the storage system (402), by rejecting management operationsassociated with the dataset (426) that are issued by a host or otherauthorized administrator, by rejecting management operations associatedwith the dataset (426) that are issued by one of the other storagesystems (404, 406) in the pod, or in some other way.

In the example method depicted in FIG. 5, the storage system (402) mayalso detect (526) that the disruption in data communications with one ormore of the other storage systems (404, 406) has been repaired. Thestorage system (402) may detect (526) that the disruption in datacommunications with one or more of the other storage systems (404, 406)has been repaired, for example, by receiving a message from the one ormore of the other storage systems (404, 406). In response to detecting(526) that the disruption in data communications with one or more of theother storage systems (404, 406) has been repaired, the storage system(402) may make (528) the dataset (426) on the particular storage system(402) accessible for management and dataset operations.

Readers will appreciate that the example depicted in FIG. 5 describes anembodiment in which various actions are depicted as occurring withinsome order, although no ordering is required. Furthermore, otherembodiments may exist where the storage system (402) only carries out asubset of the described actions. For example, the storage system (402)may perform the steps of detecting (514) a disruption in datacommunications with one or more of the other storage systems (404, 406),determining (516) whether to the particular storage system (402) shouldremain in the pod, keeping (522) the dataset (426) on the particularstorage system (402) accessible for management and dataset operations ormaking (524) the dataset (426) on the particular storage system (402)inaccessible for management and dataset operations without firstreceiving (510) a request to read a portion of the dataset (426) andprocessing (512) the request to read the portion of the dataset (426)locally. Furthermore, the storage system (402) may detect (526) that thedisruption in data communications with one or more of the other storagesystems (404, 406) has been repaired and make (528) the dataset (426) onthe particular storage system (402) accessible for management anddataset operations without first receiving (510) a request to read aportion of the dataset (426) and processing (512) the request to readthe portion of the dataset (426) locally. In fact, none of the stepsdescribed herein are explicitly required in all embodiments asprerequisites for performing other steps described herein.

For further explanation, FIG. 6 sets forth a flow chart illustratingsteps that may be performed by storage systems (402, 404, 406) thatsupport a pod according to some embodiments of the present disclosure.Although depicted in less detail, the storage systems (402, 404, 406)depicted in FIG. 6 may be similar to the storage systems described abovewith reference to FIGS. 1A-1D, FIGS. 2A-2G, FIGS. 3A-3B, FIG. 4, or anycombination thereof In fact, the storage systems (402, 404, 406)depicted in FIG. 6 may include the same, fewer, additional components asthe storage systems described above.

In the example method depicted in FIG. 6, two or more of the storagesystems (402, 404) may each identify (608) a target storage system (618)for asynchronously receiving the dataset (426). The target storagesystem (618) for asynchronously receiving the dataset (426) may beembodied, for example, as a backup storage system that is located in adifferent data center than either of the storage systems (402, 404) thatare members of a particular pod, as cloud storage that is provided by acloud services provider, or in many other ways. Readers will appreciatethat the target storage system (618) is not one of the plurality ofstorage systems (402, 404) across which the dataset (426) issynchronously replicated, and as such, the target storage system (618)initially does not include an up-to-date local copy of the dataset(426).

In the example method depicted in FIG. 6, two or more of the storagesystems (402, 404) may each also identify (610) a portion of the dataset(426) that is not being asynchronously replicated to the target storage(618) system by any of the other storages systems that are members of apod that includes the dataset (426). In such an example, the storagesystems (402, 404) may each asynchronously replicate (612), to thetarget storage system (618), the portion of the dataset (426) that isnot being asynchronously replicated to the target storage system by anyof the other storages systems. Consider an example in which a firststorage system (402) is responsible for asynchronously replicating afirst portion (e.g., a first half of an address space) of the dataset(426) to the target storage system (618). In such an example, the secondstorage system (404) would be responsible for asynchronously replicatinga second portion (e.g., a second half of an address space) of thedataset (426) to the target storage system (618), such that the two ormore storage systems (402, 404) collectively replicate the entiredataset (426) to the target storage system (618).

Readers will appreciate that through the use of pods, as describedabove, the replication relationship between two storage systems may beswitched from a relationship where data is asynchronously replicated toa relationship where data is synchronously replicated. For example, ifstorage system A is configured to asynchronously replicate a dataset tostorage system B, creating a pod that includes the dataset, storagesystem A as a member, and storage system B as a member can switch therelationship where data is asynchronously replicated to a relationshipwhere data is synchronously replicated. Likewise, through the use ofpods, the replication relationship between two storage systems may beswitched from a relationship where data is synchronously replicated to arelationship where data is asynchronously replicated. For example, if apod is created that includes the dataset, storage system A as a member,and storage system B as a member, by merely unstretching the pod (toremove storage system A as a member or to remove storage system B as amember), a relationship where data is synchronously replicated betweenthe storage systems can immediately be switched to a relationship wheredata is asynchronously replicated. In such a way, storage systems mayswitch back-and-forth as needed between asynchronous replication andsynchronous replication.

This switching can be facilitated by the implementation relying onsimilar techniques for both synchronous and asynchronous replication.For example, if resynchronization for a synchronously replicated datasetrelies on the same or a compatible mechanism as is used for asynchronousreplication, then switching to asynchronous replication is conceptuallyidentical to dropping the in-sync state and leaving a relationship in astate similar to a “perpetual recovery” mode. Likewise, switching fromasynchronous replication to synchronous replication can operateconceptually by “catching up” and becoming in-sync just as is done whencompleting a resynchronization with the switching system becoming anin-sync pod member.

Alternatively, or additionally, if both synchronous and asynchronousreplication rely on similar or identical common metadata, or a commonmodel for representing and identifying logical extents or stored blockidentities, or a common model for representing content-addressablestored blocks, then these aspects of commonality can be leveraged todramatically reduce the content that may need to be transferred whenswitching to and from synchronous and asynchronous replication. Further,if a dataset is asynchronously replicated from a storage system A to astorage system B, and system B further asynchronously replicates thatdata set to a storage system C, then a common metadata model, commonlogical extent or block identities, or common representation ofcontent-addressable stored blocks, can dramatically reduce the datatransfers needed to enable synchronous replication between storagesystem A and storage system C.

Readers will further appreciate that that through the use of pods, asdescribed above, replication techniques may be used to perform tasksother than replicating data. In fact, because a pod may include a set ofmanaged objects, tasks like migrating a virtual machine may be carriedout using pods and the replication techniques described herein. Forexample, if virtual machine A is executing on storage system A, bycreating a pod that includes virtual machine A as a managed object,storage system A as a member, and storage system B as a member, virtualmachine A and any associated images and definitions may be migrated tostorage system B, at which time the pod could simply be destroyed,membership could be updated, or other actions may be taken as necessary.

For further explanation, FIG. 7 sets forth a flow chart illustrating anexample method of establishing a synchronous replication relationshipbetween two or more storage systems (714, 724, 728) according to someembodiments of the present disclosure. Although depicted in less detail,the storage systems (714, 724, 728) depicted in FIG. 7 may be similar tothe storage systems described above with reference to FIGS. 1A-1D, FIGS.2A-2G, FIGS. 3A-3B, or any combination thereof. In fact, the storagesystems (714, 724, 728) depicted in FIG. 7 may include the same, fewer,additional components as the storage systems described above.

The example method depicted in FIG. 7 includes identifying (702), for adataset (712), a plurality of storage systems (714, 724, 728) acrosswhich the dataset (712) will be synchronously replicated. The dataset(712) depicted in FIG. 7 may be embodied, for example, as the contentsof a particular volume, as the contents of a particular shard of avolume, or as any other collection of one or more data elements. Thedataset (712) may be synchronized across a plurality of storage systems(714, 724, 728) such that each storage system (714, 724, 728) retains alocal copy of the dataset (712). In the examples described herein, sucha dataset (712) is synchronously replicated across the storage systems(714, 724, 728) in such a way that the dataset (712) can be accessedthrough any of the storage systems (714, 724, 728) with performancecharacteristics such that any one storage system in the cluster doesn'toperate substantially more optimally than any other storage system inthe cluster, at least as long as the cluster and the particular storagesystem being accessed are running nominally. In such systems,modifications to the dataset (712) should be made to the copy of thedataset that resides on each storage system (714, 724, 728) in such away that accessing the dataset (712) on any of the storage systems (714,724, 728) will yield consistent results. For example, a write requestissued to the dataset must be serviced on all storage systems (714, 724,728) or serviced on none of the storage systems (714, 724, 728).Likewise, some groups of operations (e.g., two write operations that aredirected to same location within the dataset) must be executed in thesame order on all storage systems (714, 724, 728) such that the copy ofthe dataset that resides on each storage system (714, 724, 728) isultimately identical. Modifications to the dataset (712) need not bemade at the exact same time, but some actions (e.g., issuing anacknowledgement that a write request directed to the dataset, enablingread access to a location within the dataset that is targeted by a writerequest that has not yet been completed on all storage systems) may bedelayed until the copy of the dataset (712) on each storage system (714,724, 728) has been modified.

In the example method depicted in FIG. 7, identifying (702), for adataset (712), a plurality of storage systems (714, 724, 728) acrosswhich the dataset (712) will be synchronously replicated may be carriedout, for example, by examining a pod definition or similar datastructure that associates a dataset (712) with one or more storagesystems (714, 724, 728) which nominally store that dataset (712). A‘pod’, as the term is used here and throughout the remainder of thepresent application, may be embodied as a management entity thatrepresents a dataset, a set of managed objects and managementoperations, a set of access operations to modify or read the dataset,and a plurality of storage systems. Such management operations maymodify or query managed objects equivalently through any of the storagesystems, where access operations to read or modify the dataset operateequivalently through any of the storage systems. Each storage system maystore a separate copy of the dataset as a proper subset of the datasetsstored and advertised for use by the storage system, where operations tomodify managed objects or the dataset performed and completed throughany one storage system are reflected in subsequent management objects toquery the pod or subsequent access operations to read the dataset.Additional details regarding a ‘pod’ may be found in previously filedprovisional patent application No. 62/518,071, which is incorporatedherein by reference. In such an example, the pod definition may includeat least an identification of a dataset (712) and a set of storagesystems (714, 724, 728) across which the dataset (712) is synchronouslyreplicated. Such a pod may encapsulate some of number of (perhapsoptional) properties including symmetric access, flexibleaddition/removal of replicas, high availability data consistency,uniform user administration across storage systems in relationship tothe dataset, managed host access, application clustering, and so on.Storage systems can be added to a pod, resulting in the pod's dataset(712) being copied to that storage system and then kept up to date asthe dataset (712) is modified. Storage systems can also be removed froma pod, resulting in the dataset (712) being no longer kept up to date onthe removed storage system. In such examples, a pod definition orsimilar data structure may be updated as storage systems are added toand removed from a particular pod.

The example method depicted in FIG. 7 also includes configuring (704)one or more data communications links (716, 718, 720) between each ofthe plurality of storage systems (714, 724, 728) to be used forsynchronously replicating the dataset (712). In the example methoddepicted in FIG. 6, the storage systems (714, 724, 728) in a pod mustcommunicate with each other both for high bandwidth data transfer, andfor cluster, status, and administrative communication. These distincttypes of communication could be over the same data communications links(716, 718, 720) or, in an alternative embodiment, these distinct typesof communication could be over separate data communications links (716,718, 720). In a cluster of dual controller storage systems, bothcontrollers in each storage system should have the nominal ability tocommunicate with both controllers for any paired storage systems (i.e.,any other storage system in a pod).

In a primary/secondary controller design, all cluster communication foractive replication may run between primary controllers until a faultoccurs. In such systems, some communication may occur between a primarycontroller and a secondary controller, or between secondary controllerson distinct storage systems, in order to verify that the datacommunications links between such entities are operational. In othercases, virtual network addresses might be used to limit theconfiguration needed for of inter-datacenter network links, or tosimplify design of the clustered aspect of the storage system. In anactive/active controller design, cluster communications might run fromall active controllers of one storage system to some or all activecontrollers in any paired storage systems, or they might be filteredthrough a common switch, or they might use a virtual network address tosimplify configuration, or they might use some combination. In ascale-out design, two or more common network switches may be used suchthat all scale-out storage controllers within the storage system connectto the network switches in order to handle data traffic. The switchesmight or might not use techniques to limit the number of exposed networkaddresses, so that paired storage systems don't need to be configuredwith the network addresses of all storage controllers.

In the example method depicted in FIG. 7, configuring (704) one or moredata communications links (716, 718, 720) between each of the pluralityof storage systems (714, 724, 728) to be used for synchronouslyreplicating the dataset (712) may be carried out, for example, byconfiguring the storage systems (716, 718, 720) to communicate viadefined ports over a data communications network, by configuring thestorage systems (716, 718, 720) to communicate over a point-to-pointdata communications link between two of the storage systems (716, 724,728), or in a variety of ways. If secure communication is required, someform of key exchange may be needed, or communication could be done orbootstrapped through some service such as SSH (Secure SHell), SSL, orsome other service or protocol built around public keys orDiffie-Hellman key exchange or reasonable alternatives. Securecommunications could also be mediated through some vendor-provided cloudservice tied in some way to customer identities. Alternately, a serviceconfigured to run on customer facilities, such as running in a virtualmachine or container, could be used to mediate key exchanges necessaryfor secure communications between replicating storage systems (716, 718,720). Readers will appreciate that a pod including more than two storagesystems may need communication links between most or all of theindividual storage systems. In the example depicted in FIG. 6, threedata communications links (716, 718, 720) are illustrated, althoughadditional data communications links may exist in other embodiments.

Readers will appreciate that communication between the storage systems(714, 724, 728) across which the dataset (712) will be synchronouslyreplicated serves some number of purposes. One purpose, for example, isto deliver data from one storage system (714, 724, 728) to anotherstorage system (714, 724, 728) as part of I/O processing. For example,processing a write commonly requires delivering the write content andsome description of the write to any paired storage systems for a pod.Another purpose served by data communications between the storagesystems (714, 724, 728) may be to communicate configuration changes andanalytics data in order to handle creating, extending, deleting orrenaming volumes, files, object buckets, and so on. Another purposeserved by data communications between the storage systems (714, 724,728) may be to carry out communication involved in detecting andhandling storage system and interconnect faults. This type ofcommunication may be time critical and may need to be prioritized toensure it doesn't get stuck behind a long network queue delay when alarge burst of write traffic is suddenly dumped on the datacenterinterconnect.

Readers will further appreciate that different types of communicationmay use the same connections, or different connections, and may use thesame networks, or different networks, in various combinations. Further,some communications may be encrypted and secured while othercommunications might not be encrypted. In some cases, the datacommunications links could be used to forward I/O requests (eitherdirectly as the requests themselves or as logical descriptions of theoperations the I/O requests represent) from one storage system toanother. This could be used, for example, in cases where one storagesystem has up-to-date and in-sync content for a pod, and another storagesystem does not currently have up-to-date and in-sync content for thepod. In such cases, as long as the data communications links arerunning, requests can be forwarded from the storage system that is notup-to-date and in-sync to the storage system that is up-to-date andin-sync.

The example method depicted in FIG. 7 also includes exchanging (706),between the plurality of storage systems (714, 724, 728), timinginformation (710, 722, 726) for at least one of the plurality of storagesystems (714, 724, 728). In the example method depicted in FIG. 6,timing information (710, 722, 726) for a particular storage system (714,724, 728) may be embodied, for example, as the value of a clock withinthe storage system (714, 724, 728). In an alternative embodiment, thetiming information (710, 722, 726) for a particular storage system (714,724, 728) may be embodied as a value which serves as a proxy for a clockvalue. The value which serves as a proxy for a clock value may beincluded in a token that is exchanged between the storage systems. Sucha value which serves as a proxy for a clock value may be embodied, forexample, a sequence number that a particular storage system (714, 724,728) or storage system controller can internally record as having beensent at a particular time. In such an example, if the token (e.g., thesequence number) is received back, the associated clock value can befound and utilized as the basis for determining whether a valid lease isstill in place. In the example method depicted in FIG. 6, exchanging(706) timing information (710, 722, 726) for at least one of theplurality of storage systems (714, 724, 728) between the plurality ofstorage systems (714, 724, 728) may be carried out, for example, by eachstorage system (714, 724, 728) sending timing information to each otherstorage system (714, 724, 728) in a pod on a periodic basis, on demand,within a predetermined amount of time after a lease is established,within a predetermined amount of time before a lease is set to expire,as part of an attempt to initiate or re-establish a synchronousreplication relationship, or in some other way.

The example method depicted in FIG. 7 also includes establishing (708),in dependence upon the timing information (710, 722, 726) for at leastone of the plurality of storage systems (714, 724, 728), a synchronousreplication lease, the synchronous replication lease identifying aperiod of time during which the synchronous replication relationship isvalid. In the example method depicted in FIG. 7, a synchronousreplication relationship is formed as a set of storage systems (714,724, 728) that replicate some dataset (712) between these largelyindependent stores, where each storage systems (714, 724, 728) has itsown copy and its own separate internal management of relevant datastructures for defining storage objects, for mapping objects to physicalstorage, for deduplication, for defining the mapping of content tosnapshots, and so on. A synchronous replication relationship can bespecific to a particular dataset, such that a particular storage system(714, 724, 728) may be associated with more than one synchronousreplication relationship, where each synchronous replicationrelationship is differentiated by the dataset being described and mayfurther consist of a different set of additional member storage systems.

In the example method depicted in FIG. 7, a synchronous replicationlease may be established (708) in dependence upon the timing information(710, 722, 726) for at least one of the plurality of storage systems(714, 724, 728) in a variety of different ways. In one embodiment, thestorage systems may establish (708) a synchronous replication lease byutilizing the timing information (710, 722, 726) for each of theplurality of storage systems (714, 724, 728) to coordinate clocks. Insuch an example, once the clocks are coordinated for each of the storagesystems (714, 724, 728), the storage system may establish (708) asynchronous replication lease that extends for a predetermined period oftime beyond the coordinated clock values. For example, if the clocks foreach storage system (714, 724, 728) are coordinated to be at a value ofX, the storage systems (714, 724, 728) may each be configured toestablish a synchronous replication lease that is valid until X+2seconds.

In an alternative embodiment, the need to coordinate clocks between thestorage systems (714, 724, 728) may be avoided while still achieving atiming guarantee. In such an embodiment, a storage controller withineach storage system (714, 724, 728) may have a local monotonicallyincreasing clock. A synchronous replication lease may be established(708) between storage controllers (such as a primary controller in onestorage system communicating with a primary controller in a pairedstorage system) by each controller sending its clock value to the otherstorage controllers along with the last clock value it received from theother storage controller. When a particular controller receives back itsclock value from another controller, it adds some agreed upon leaseinterval to that received clock value and uses that to establish (708)its local synchronous replication lease. In such a way, the synchronousreplication lease may be calculated in dependence upon a value of alocal clock that was received from another storage system.

Consider an example in which a storage controller in a first storagesystem (714) is communicating with a storage controller in a secondstorage system (724). In such an example, assume that the value of themonotonically increasing clock for the storage controller in the firststorage system (714) is 1000 milliseconds. Further assume that thestorage controller in the first storage system (714) sends a message tothe storage controller in the second storage system (724) indicatingthat its clock value at the time that the message was generated was 1000milliseconds. In such an example, assume that 500 milliseconds after thestorage controller in the first storage system (714) sent a message tothe storage controller in the second storage system (724) indicatingthat its clock value at the time that the message was generated was 1000milliseconds, the storage controller in the first storage system (714)receives a message from the storage controller in a second storagesystem (724) indicating that: 1) the value of the monotonicallyincreasing clock in the storage controller in the second storage system(724) was at a value of 5000 milliseconds when the message wasgenerated, and 2) the last value of the monotonically increasing clockin the storage controller in the first storage system (714) that wasreceived by the second storage system (724) was 1000 milliseconds. Insuch an example, if the agreed upon lease interval is 2000 milliseconds,the first storage system (714) will establish (708) a synchronousreplication lease that is valid until the monotonically increasing clockfor the storage controller in the first storage system (714) is at avalue of 3000 milliseconds. If the storage controller in the firststorage system (714) does not receive a message from the storagecontroller in the second storage system (724) that includes an updatedvalue of the monotonically increasing clock for the storage controllerin the first storage system (714) by the time that the monotonicallyincreasing clock for the storage controller in the first storage system(714) reaches a value of 3000 milliseconds, the first storage system(714) will treat the synchronous replication lease to have expired andmay take various actions as described in greater detail below. Readerswill appreciate that storage controllers within the remaining storagesystems (724, 728) in a pod may react similarly and perform a similartracking and updating of the synchronous replication lease. Essentially,the receiving controller can be assured that the network and the pairedcontrollers were running somewhere during that time interval, and it canbe assured that the paired controller received a message that it sentsomewhere during that time interval. Without any coordination in clocks,the receiving controller can't know exactly where in that time intervalthe network and the paired controller were running, and can't reallyknow if there were queue delays in sending its clock value or inreceiving back its clock value.

In a pod consisting of two storage systems, each with a simple primarycontroller, where the primary controllers are exchanging clocks as partof their cluster communication, each primary controller can use theactivity lease to put a bound on when it won't know for certain that thepaired controller was running. At the point it becomes uncertain (whenthe controller's connection's activity lease has expired), it can startsending messages indicating that it is uncertain and that a properlysynchronized connection must be reestablished before activity leases canagain be resumed. These messages may be received and responses may notbe received, if the network is working in one direction but is notworking properly in the other direction. This may be the firstindication by a running paired controller that the connection isn'trunning normally, because its own activity lease may not yet haveexpired, due to a different combination of lost messages and queuedelays. As a result, if such a message is received, it should alsoconsider its own activity lease to be expired, and it should startsending messages of its own attempting to coordinate synchronizing theconnection and resuming of activity leases. Until that happens and a newset of clock exchanges can succeed, neither controller can consider itsactivity lease to be valid.

In this model, a controller can wait for lease interval seconds after itstarted sending reestablish messages, and if it hasn't received aresponse, it can be assured that either the paired controller is down orthe paired controller's own lease for the connection will have expired.To handle minor amounts of clock drift, it may wait slightly longer thanthe lease interval (i.e., a reestablishment lease). When a controllerreceives a reestablish message, it could consider the reestablishmentlease to be expired immediately, rather than waiting (since it knowsthat the sending controller's activity lease has expired), but it willoften make sense to attempt further messaging before giving up, in casemessage loss was a temporary condition caused, for example, by acongested network switch.

In an alternative embodiment, in addition to establishing a synchronousreplication lease, a cluster membership lease may also be establishedupon receipt of a clock value from a paired storage system or uponreceipt back of a clock exchanged with a paired storage system. In suchan example, each storage system may have its own synchronous replicationlease and its own cluster membership lease with every paired storagesystem. The expiration of a synchronous replication lease with any pairmay result in paused processing. Cluster membership, however, cannot berecalculated until the cluster membership lease has expired with allpairs. As such, the duration of the cluster membership lease should beset, based on the message and clock value interactions, to ensure thatthe cluster membership lease with a pair will not expire until after apair's synchronous replication link for that link has expired. Readerswill appreciate that a cluster membership lease can be established byeach storage system in a pod and may be associated with a communicationlink between any two storage systems that are members of the pod.Furthermore, the cluster membership lease may extend after theexpiration of the synchronous replication lease for a duration of timethat is at least as long as the time period for expiration of thesynchronous replication lease. The cluster membership lease may beextended on receipt of a clock value received from a paired storagesystem as part of a clock exchange, where the cluster membership leaseperiod from the current clock value may be at least as long as theperiod established for the last synchronous replication lease extensionbased on exchanged clock values. In additional embodiments, additionalcluster membership information can be exchanged over a connection,including when a session is first negotiated. Readers will appreciatethat in embodiments that utilize a cluster membership lease, eachstorage system (or storage controller) may have its own value for thecluster membership lease. Such a lease should not expire until it can beassured that all synchronous replication leases across all pod memberswill have expired given that the cluster lease expiration allowsestablishing new membership such as through a mediator race and thesynchronous replication lease expiration forces processing of newrequests to pause. In such an example, the pause must be assured to bein place everywhere before cluster membership actions can be taken.

Readers will appreciate that although only one of the storage systems(714) is depicted as identifying (702), for a dataset (712), a pluralityof storage systems (714, 724, 728) across which the dataset (712) willbe synchronously replicated, configuring (704) one or more datacommunications links (716, 718, 720) between each of the plurality ofstorage systems (714, 724, 728) to be used for synchronously replicatingthe dataset (712), exchanging (706), between the plurality of storagesystems (714, 724, 728), timing information (710, 722, 726) for at leastone of the plurality of storage systems (714, 724, 728), andestablishing (708), in dependence upon the timing information (710, 722,726) for at least one of the plurality of storage systems (714, 724,728), a synchronous replication lease, the remaining storage systems(724, 728) may also carry out such steps. In fact, all three storagesystems (714, 724, 728) may carry out one or more of the steps describedabove at the same time, as establishing a synchronous replicationrelationship between two or more storage systems (714, 724, 728) mayrequire collaboration and interaction between two or more storagesystems (714, 724, 728).

For further explanation, FIG. 8 sets forth an example of a hybridstorage system for synchronously replicating datasets across acloud-based storage system (803) and multiple, physical storage systems(402, 404 . . . 406) implemented similarly to the storage systemsdescribed in FIGS. 4-7, and in accordance with some embodiments of thepresent disclosure.

In the example depicted in FIG. 8, the cloud-based storage system (803)is created entirely in a cloud computing environment (852) such as, forexample, Amazon Web Services (‘AWS’), Microsoft Azure, Google CloudPlatform, IBM Cloud, Oracle Cloud, and others. The cloud-based storagesystem (803) may be used to provide services similar to the servicesthat may be provided by the storage systems described above.

Further, in this example, the physical storage systems (402, 404 . . .406) may include some or all of the components described above withreference to FIGS. 1A-7.

As depicted in the hybrid configuration of FIG. 8, one or more datasets(426, 428) may be synchronously replicated among the physical storagesystems (402, 404 . . . 406) and also among the cloud-based storagesystem (803) implemented within a remote cloud computing environment(852) that is connected across a network (850), such as the Internet. Inthis example, there are two datasets (426, 428) that correspond to tworespective pods (853, 854), where the pods (853, 854) include allfeatures and functionality described above with reference to FIGS. 1A-7.

However, in other examples, not depicted, a hybrid configuration maysynchronously replicate datasets across one or more physical storagesystems (402, 404 . . . 406) and also across a virtual machine basedimplementation of a storage system, such as a virtual machine basedimplementation of storage systems (306) described above with referenceto FIGS. 1A-7. Further, in this example of a hybrid configuration, thevirtual machine based implementation of a storage system may be on asame network as the physical storage systems (402, 404 . . . 406), orthe virtual machine based storage system may be at a remote location andconnected across a wide area network.

In the depiction of FIG. 8, one or more datasets (426, 428) aresynchronously replicated between the cloud-based storage system (803)and the physical storage systems (402, 404 . . . 406) similarly to thesynchronously replicated datasets among only the physical storagesystems (402, 404 . . . 406).

However, in other examples, one or more datasets (426, 428) may besynchronously replicated among the physical storage systems (402, 404 .. . 406), but where the one or more datasets (426, 428) areasynchronously stored at the cloud-based storage system (803).

In this way, in the event of a failure or in the event of a request toreconstruct or clone one or more pods (853, 854), the recovery,reconstruction, or cloning may be performed using only data stored onthe cloud-based storage system (803) as a source storage system suchthat a target storage system, whether virtual of physical, may be usedto resume operation of the original storage systems within the contextof any prior replication or other relationship for the dataset.

Further, in this example, a target storage system may be one or morephysical storage systems, such as storage system (306), or where atarget storage system may be another cloud-based storage system, such ascloud-based storage system (803).

For further explanation, FIG. 9 sets forth an example of an additionalcloud-based storage system (902) in accordance with some embodiments ofthe present disclosure. In the example depicted in FIG. 50, thecloud-based storage system (902) is created entirely in a cloudcomputing environment (900) such as, for example, Amazon Web Services(‘AWS’), Microsoft Azure, Google Cloud Platform, IBM Cloud, OracleCloud, and others. The cloud-based storage system (902) may be used toprovide services similar to the services that may be provided by thestorage systems described above. For example, the cloud-based storagesystem (902) may be used to provide block storage services to users ofthe cloud-based storage system (902), the cloud-based storage system(902) may be used to provide storage services to users of thecloud-based storage system (902) through the use of solid-state storage,and so on.

The cloud-based storage system (902) depicted in FIG. 50 may operate ina manner that is somewhat similar to the cloud-based storage system(902) depicted in FIG. 49, as the cloud-based storage system (902)depicted in FIG. 50 includes a storage controller application (906) thatis being executed in a cloud computing instance (904). In the exampledepicted in FIG. 50, however, the cloud computing instance (904) thatexecutes the storage controller application (906) is a cloud computinginstance (904) with local storage (908). In such an example, datawritten to the cloud-based storage system (902) may be stored in boththe local storage (908) of the cloud computing instance (904) and alsoin cloud-based object storage (910) in the same manner that thecloud-based object storage (910) was used above. In some embodiments,for example, the storage controller application (906) may be responsiblefor writing data to the local storage (908) of the cloud computinginstance (904) while a software daemon (912) may be responsible forensuring that the data is written to the cloud-based object storage(910) in the same manner that the cloud-based object storage (910) wasused above.

Readers will appreciate that a cloud-based storage system (902) depictedin FIG. 50 may represent a less expensive, less robust version of acloud-based storage system than was depicted in FIG. 49. In yetalternative embodiments, the cloud-based storage system (902) depictedin FIG. 50 could include additional cloud computing instances with localstorage that supported the execution of the storage controllerapplication (906), such that failover can occur if the cloud computinginstance (904) that executes the storage controller application (906)fails. Likewise, in other embodiments, the cloud-based storage system(902) depicted in FIG. 50 can include additional cloud computinginstances with local storage to expand the amount local storage that isoffered by the cloud computing instances in the cloud-based storagesystem (902).

Readers will appreciate that many of the failure scenarios describedabove with reference to FIG. 49 would also apply to cloud-based storagesystem (902) depicted in FIG. 50. Likewise, the cloud-based storagesystem (902) depicted in FIG. 50 may be dynamically scaled up and downin a similar manner as described above. The performance of varioussystem-level tasks may also be executed by the cloud-based storagesystem (902) depicted in FIG. 50 in an intelligent way, as describedabove.

Readers will appreciate that, in an effort to increase the resiliency ofthe cloud-based storage systems described above, various components maybe located within different availability zones. For example, a firstcloud computing instance that supports the execution of the storagecontroller application may be located within a first availability zonewhile a second cloud computing instance that also supports the executionof the storage controller application may be located within a secondavailability zone. Likewise, the cloud computing instances with localstorage may be distributed across multiple availability zones. In fact,in some embodiments, an entire second cloud-based storage system couldbe created in a different availability zone, where data in the originalcloud-based storage system is replicated (synchronously orasynchronously) to the second cloud-based storage system so that if theentire original cloud-based storage system went down, a replacementcloud-based storage system (the second cloud-based storage system) couldbe brought up in a trivial amount of time.

Readers will appreciate that the cloud-based storage systems describedherein may be used as part of a fleet of storage systems. In fact, thecloud-based storage systems described herein may be paired withon-premises storage systems. In such an example, data stored in theon-premises storage may be replicated (synchronously or asynchronously)to the cloud-based storage system, and vice versa.

For further explanation, FIG. 10 sets forth a flow chart illustrating anexample method of servicing I/O operations in a cloud-based storagesystem (1004). Although depicted in less detail, the cloud-based storagesystem (1004) depicted in FIG. 6 may be similar to the cloud-basedstorage systems described above and may be supported by a cloudcomputing environment (1002).

The example method depicted in FIG. 10 includes receiving (1006), by thecloud-based storage system (1004), a request to write data to thecloud-based storage system (1004). The request to write data may bereceived, for example, from an application executing in the cloudcomputing environment, by a user of the storage system that iscommunicatively coupled to the cloud computing environment, and in otherways. In such an example, the request can include the data that is to bewritten to the cloud-based storage system (1004). In other embodiments,the request to write data to the cloud-based storage system (1004) mayoccur at boot-time when the cloud-based storage system (1004) is beingbrought up.

The example method depicted in FIG. 10 also includes deduplicating(1008) the data. Data deduplication is a data reduction technique foreliminating duplicate copies of repeating data. The cloud-based storagesystem (1004) may deduplicate (1008) the data, for example, by comparingone or more portions of the data to data that is already stored in thecloud-based storage system (1004), by comparing a fingerprint for one ormore portions of the data to fingerprints for data that is alreadystored in the cloud-based storage system (1004), or in other ways. Insuch an example, duplicate data may be removed and replaced by areference to an already existing copy of the data that is already storedin the cloud-based storage system (1004).

The example method depicted in FIG. 10 also includes compressing (1010)the data. Data compression is a data reduction technique wherebyinformation is encoded using fewer bits than the originalrepresentation. The cloud-based storage system (1004) may compress(1010) the data by applying one or more data compression algorithms tothe data, which at this point may not include data that data that isalready stored in the cloud-based storage system (1004).

The example method depicted in FIG. 10 also includes encrypting (1012)the data. Data encryption is a technique that involves the conversion ofdata from a readable format into an encoded format that can only be reador processed after the data has been decrypted. The cloud-based storagesystem (1004) may encrypt (1012) the data, which at this point may havealready been deduplicated and compressed, using an encryption key.Readers will appreciate that although the embodiment depicted in FIG. 10involves deduplicating (1008) the data, compressing (1010) the data, andencrypting (1012) the data, other embodiments exist in which fewer ofthese steps are performed and embodiment exist in which the same numberof steps or fewer are performed in a different order.

The example method depicted in FIG. 10 also includes storing (1014), insolid-state storage of the cloud-based storage system (1004), the data.Storing (1014) the data in solid-state storage of the cloud-basedstorage system (1004) may be carried out, for example, by storing (1016)the data in local storage (e.g., SSDs) of one or more cloud computinginstances, as described in more detail above. In such an example, thedata may be spread across the local storage of many cloud computinginstances, along with parity data, to implement RAID or RAID-like dataredundancy.

The example method depicted in FIG. 10 also includes storing (1018), inobject-storage of the cloud-based storage system (1004), the data.Storing (1018) the data in object-storage of the cloud-based storagesystem can include creating (1020) one or more equal sized objects,wherein each equal sized object includes a distinct chunk of the data,as described in greater detail above.

The example method depicted in FIG. 10 also includes receiving (1022),by the cloud-based storage system, a request to read data from thecloud-based storage system (1004). The request to read data from thecloud-based storage system (1004) may be received, for example, from anapplication executing in the cloud computing environment, by a user ofthe storage system that is communicatively coupled to the cloudcomputing environment, and in other ways. The request can include, forexample, a logical address the data that is to be read from thecloud-based storage system (1004).

The example method depicted in FIG. 10 also includes retrieving (1024),from solid-state storage of the cloud-based storage system (1004), thedata. Readers will appreciate that the cloud-based storage system (1004)may retrieve (1024) the data from solid-state storage of the cloud-basedstorage system (1004), for example, by the storage controllerapplication forwarding the read request to the cloud computing instancethat includes the requested data in its local storage. Readers willappreciate that by retrieving (1024) the data from solid-state storageof the cloud-based storage system (1004), the data may be retrieved morerapidly than if the data were read from cloud-based object storage, eventhough the cloud-based object storage does include a copy of the data.

For further explanation, FIG. 11 sets forth a flow chart illustrating anadditional example method of servicing I/O operations in a cloud-basedstorage system (1004). The example method depicted in FIG. 11 is similarto the example method depicted in FIG. 10, as the example methoddepicted in FIG. 11 also includes receiving (1006) a request to writedata to the cloud-based storage system (1004), storing (1014) the datain solid-state storage of the cloud-based storage system (1004), andstoring (1018) the data in object-storage of the cloud-based storagesystem (1004).

The example method depicted in FIG. 11 also includes detecting (1102)that at least some portion of the solid-state storage of the cloud-basedstorage system has become unavailable. Detecting (1102) that at leastsome portion of the solid-state storage of the cloud-based storagesystem has become unavailable may be carried out, for example, bydetecting that one or more of the cloud computing instances thatincludes local storage has become unavailable, as described in greaterdetail below.

The example method depicted in FIG. 11 also includes identifying (1104)data that was stored in the portion of the solid-state storage of thecloud-based storage system that has become unavailable. Identifying(1104) data that was stored in the portion of the solid-state storage ofthe cloud-based storage system that has become unavailable may becarried out, for example, through the use of metadata that maps someidentifier of a piece of data (e.g., a sequence number, an address) tothe location where the data is stored. Such metadata, or separatemetadata, may also map the piece of data to one or more objectidentifiers that identify objects stored in the object-storage of thecloud-based storage system that contain the piece of data.

The example method depicted in FIG. 11 also includes retrieving (1106),from object-storage of the cloud-based storage system, the data that wasstored in the portion of the solid-state storage of the cloud-basedstorage system that has become unavailable. Retrieving (1106) the datathat was stored in the portion of the solid-state storage of thecloud-based storage system that has become unavailable fromobject-storage of the cloud-based storage system may be carried out, forexample, through the use of metadata described above that maps the datathat was stored in the portion of the solid-state storage of thecloud-based storage system that has become unavailable to one or moreobjects stored in the object-storage of the cloud-based storage systemthat contain the piece of data. In such an example, retrieving (1106)the data may be carried out by reading the objects that map to the datafrom the object-storage of the cloud-based storage system.

The example method depicted in FIG. 11 also includes storing (1108), insolid-state storage of the cloud-based storage system, the retrieveddata. Storing (1108) the retrieved data in solid-state storage of thecloud-based storage system may be carried out, for example, by creatingreplacement cloud computing instances with local storage and storing thedata in the local storage of one or more of the replacement cloudcomputing instances, as described in greater detail above.

Readers will appreciate that although the embodiments described aboverelate to embodiments in which data that was stored in the portion ofthe solid-state storage of the cloud-based storage system that hasbecome unavailable is essentially brought back into the solid-statestorage layer of the cloud-based storage system by retrieving the datafrom the object-storage layer of the cloud-based storage system, otherembodiments are within the scope of the present disclosure. For example,because data may be distributed across the local storage of multiplecloud computing instances using data redundancy techniques such as RAID,in some embodiments the lost data may be brought back into thesolid-state storage layer of the cloud-based storage system through aRAID rebuild.

For further explanation, FIG. 12 sets forth a flow chart illustrating anexample method of servicing I/O operations in a cloud-based storagesystem (1204). Although depicted in less detail, the cloud-based storagesystem (1204) depicted in FIG. 12 may be similar to the cloud-basedstorage systems described above and may be supported by a cloudcomputing environment (1202).

The example method depicted in FIG. 12 includes receiving (1206), by thecloud-based storage system (1204), a request to write data to thecloud-based storage system (1204). The request to write data may bereceived, for example, from an application executing in the cloudcomputing environment, by a user of the storage system that iscommunicatively coupled to the cloud computing environment, and in otherways. In such an example, the request can include the data that is to bewritten to the cloud-based storage system (1204). In other embodiments,the request to write data to the cloud-based storage system (1204) mayoccur at boot-time when the cloud-based storage system (1204) is beingbrought up.

The example method depicted in FIG. 12 also includes deduplicating(1208) the data. Data deduplication is a data reduction technique foreliminating duplicate copies of repeating data. The cloud-based storagesystem (1204) may deduplicate (1208) the data, for example, by comparingone or more portions of the data to data that is already stored in thecloud-based storage system (1204), by comparing a fingerprint for one ormore portions of the data to fingerprints for data that is alreadystored in the cloud-based storage system (1204), or in other ways. Insuch an example, duplicate data may be removed and replaced by areference to an already existing copy of the data that is already storedin the cloud-based storage system (1204).

The example method depicted in FIG. 12 also includes compressing (1210)the data. Data compression is a data reduction technique wherebyinformation is encoded using fewer bits than the originalrepresentation. The cloud-based storage system (1204) may compress(1210) the data by applying one or more data compression algorithms tothe data, which at this point may not include data that data that isalready stored in the cloud-based storage system (1204).

The example method depicted in FIG. 12 also includes encrypting (1212)the data. Data encryption is a technique that involves the conversion ofdata from a readable format into an encoded format that can only be reador processed after the data has been decrypted. The cloud-based storagesystem (1204) may encrypt (1212) the data, which at this point may havealready been deduplicated and compressed, using an encryption key.Readers will appreciate that although the embodiment depicted in FIG. 12involves deduplicating (1208) the data, compressing (1210) the data, andencrypting (1212) the data, other embodiments exist in which fewer ofthese steps are performed and embodiment exist in which the same numberof steps or fewer are performed in a different order.

The example method depicted in FIG. 12 also includes storing (1214), inblock-storage of the cloud-based storage system (1204), the data.Storing (1214) the data in block-storage of the cloud-based storagesystem (1204) may be carried out, for example, by storing (1216) thedata in local storage (e.g., SSDs) of one or more cloud computinginstances, as described in more detail above. In such an example, thedata spread across local storage of multiple cloud computing instances,along with parity data, to implement RAID or RAID-like data redundancy.

The example method depicted in FIG. 12 also includes storing (1218), inobject-storage of the cloud-based storage system (1204), the data.Storing (1218) the data in object-storage of the cloud-based storagesystem can include creating (1220) one or more equal sized objects,wherein each equal sized object includes a distinct chunk of the data,as described in greater detail above.

The example method depicted in FIG. 12 also includes receiving (1222),by the cloud-based storage system, a request to read data from thecloud-based storage system (1204). The request to read data from thecloud-based storage system (1204) may be received, for example, from anapplication executing in the cloud computing environment, by a user ofthe storage system that is communicatively coupled to the cloudcomputing environment, and in other ways. The request can include, forexample, a logical address the data that is to be read from thecloud-based storage system (1204).

The example method depicted in FIG. 12 also includes retrieving (1224),from block-storage of the cloud-based storage system (1204), the data.Readers will appreciate that the cloud-based storage system (1204) mayretrieve (1224) the data from block-storage of the cloud-based storagesystem (1204), for example, by the storage controller applicationforwarding the read request to the cloud computing instance thatincludes the requested data in its local storage. Readers willappreciate that by retrieving (1224) the data from block-storage of thecloud-based storage system (1204), the data may be retrieved morerapidly than if the data were read from cloud-based object storage, eventhough the cloud-based object storage does include a copy of the data.

For further explanation, FIG. 13 sets forth a flow chart illustrating anadditional example method of servicing I/O operations in a cloud-basedstorage system (1204). The example method depicted in FIG. 13 is similarto the example method depicted in FIG. 12, as the example methoddepicted in FIG. 13 also includes receiving (1206) a request to writedata to the cloud-based storage system (1204), storing (1214) the datain block-storage of the cloud-based storage system (1204), and storing(1218) the data in object-storage of the cloud-based storage system(1204).

The example method depicted in FIG. 13 also includes detecting (1302)that at least some portion of the block-storage of the cloud-basedstorage system has become unavailable. Detecting (1302) that at leastsome portion of the block-storage of the cloud-based storage system hasbecome unavailable may be carried out, for example, by detecting thatone or more of the cloud computing instances that includes local storagehas become unavailable, as described in greater detail below.

The example method depicted in FIG. 13 also includes identifying (1304)data that was stored in the portion of the block-storage of thecloud-based storage system that has become unavailable. Identifying(1304) data that was stored in the portion of the block-storage of thecloud-based storage system that has become unavailable may be carriedout, for example, through the use of metadata that maps some identifierof a piece of data (e.g., a sequence number, an address) to the locationwhere the data is stored. Such metadata, or separate metadata, may alsomap the piece of data to one or more object identifiers that identifyobjects stored in the object-storage of the cloud-based storage systemthat contain the piece of data.

The example method depicted in FIG. 13 also includes retrieving (1306),from object-storage of the cloud-based storage system, the data that wasstored in the portion of the block-storage of the cloud-based storagesystem that has become unavailable. Retrieving (1306) the data that wasstored in the portion of the block-storage of the cloud-based storagesystem that has become unavailable from object-storage of thecloud-based storage system may be carried out, for example, through theuse of metadata described above that maps the data that was stored inthe portion of the block-storage of the cloud-based storage system thathas become unavailable to one or more objects stored in theobject-storage of the cloud-based storage system that contain the pieceof data. In such an example, retrieving (1306) the data may be carriedout by reading the objects that map to the data from the object-storageof the cloud-based storage system.

The example method depicted in FIG. 13 also includes storing (1308), inblock-storage of the cloud-based storage system, the retrieved data.Storing (1308) the retrieved data in block-storage of the cloud-basedstorage system may be carried out, for example, by creating replacementcloud computing instances with local storage and storing the data in thelocal storage of one or more of the replacement cloud computinginstances, as described in greater detail above.

Readers will appreciate that although the embodiments described aboverelate to embodiments in which data that was stored in the portion ofthe block-storage of the cloud-based storage system that has becomeunavailable is essentially brought back into the block-storage layer ofthe cloud-based storage system by retrieving the data from theobject-storage layer of the cloud-based storage system, otherembodiments are within the scope of the present disclosure. For example,because data may be distributed across the local storage of multiplecloud computing instances using data redundancy techniques such as RAID,in some embodiments the lost data may be brought back into theblock-storage layer of the cloud-based storage system through a RAIDrebuild.

For further explanation, FIG. 14 sets forth a flow chart illustrating anexample method for recovery for a cloud-based storage system (1400A)synchronously replicating a dataset according to some embodiments of thepresent disclosure.

As illustrated in FIG. 14, the storage systems (1400A-1400N)synchronously replicating a dataset (1458) include both hardware-basedstorage systems (1400B-1400N) and a cloud-based storage system (1400A)implemented within a cloud computing environment (1401). For clarity,only one cloud-based storage system (1400A) is depicted, however, inother examples, there may be multiple cloud-based storage systems, ormultiple cloud-based storage systems without any hardware-based storagesystems.

In this examples, the cloud-based storage system (1400A) may providesimilar services as those described for the cloud-based storage systemsabove, with reference to FIGS. 8-13. For example, the cloud-basedstorage system (1400A) may be used to provide block storage services tousers based on use of services of a cloud-computing environment, such ascloud computing environments described in FIGS. 8-13, including storageprovided by virtual computing instances or storage provided bysolid-state storage, and so on. Further, the cloud computing environment(1401) may be implemented similarly to the cloud computing environmentsdescribed above with reference to FIGS. 8-13.

In some implementations, a cloud-based storage system may store data inmultiple tiers of cloud storage, including a first tier of block storagewithin a cloud computing instance layer that includes respective localstorage and a second tier of object storage within a cloud-based objectstorage. For example, with reference to FIG. 3D, a first tier of cloudstorage may include cloud computing instances (340 a-340 n), whererespective cloud computing instances may include respective storage(330, 342, 334, 344, 338, 346), and where the types of storage aredescribed above. Further, in this example, a second tier of cloudstorage may be a cloud-based object store (348), as also described abovewith reference to FIG. 3D.

In some examples, a first tier of cloud storage may serve as a cache ofa second tier of cloud storage, and in such a case, the entire contentof the first tier of cloud storage may be reconstructed from the secondtier of cloud storage. In other examples, a first tier of cloud storagemay include some updates not in the second tier of cloud storage or thefirst tier of cloud storage may include some updates that are not yet inthe second tier of cloud storage, and in response, most, but notnecessarily all, of the content in the first tier of cloud storage maybe reconstructed from the second tier of cloud storage. In some cases,suitable interaction in the data between the first tier of cloud storageand the second tier of cloud storage may ensure that the content of thesecond tier of cloud storage is appropriately consistent.

Further, in some implementations, cloud computing instances for acloud-based storage system may supply partial front-end datasets for acomplete, or “bulk”, dataset stored using cloud storage infrastructure,such as object storage. In this case, a cloud computing instance may beconsidered to be, more generically, a virtual machine that executesparts of the cloud-based storage system (1400A) implementation.Continuing with this example, it may be necessary for these parts of thecloud-based storage system (1400A) to reach a consensus that theunderlying virtual machine(s) are operating to implement a singlevirtual storage system in accordance with the rest of this model. Insome examples, the cloud computing environment (316) or cloudinfrastructure may supply alternate models for ensuring that the virtualmachines, high performance storage, and bulk storage used to create asingle cloud-based storage system (1400A) is operationally consistentand can interact coherently as a storage system, such as the storagesystems described within FIGS. 1A-8.

In this example, the storage systems (1400A-1400N) depicted in FIG. 14may be similar to the storage systems described above with reference toFIGS. 1A-1D, FIGS. 2A-2G, FIGS. 3A-3D, FIG. 8-13, or any combinationthereof. In fact, the storage systems (1400A-1400N) depicted in FIG. 14may include the same, fewer, or additional components as the storagesystems described above.

In some implementations, multiple storage systems (1400A-1400N) that aresynchronously replicating a dataset (1458) may be in communication witheach other during normal operation for receiving and processing requests(1452) from a host (1451) computing device. However, in some instances,one or more of the storage systems (1400A-1400N) may fail, restart,upgrade or otherwise be unavailable. Recovery in this context is theprocess of making in-sync pod member storage systems consistent after afault or some other service outage causes at least one of the in-syncstorage systems to be interrupted and possibly lose the context ofin-flight operations.

In some implementations, a ‘pod’, as the term is used here andthroughout the remainder of the present application, may be embodied asa management entity that represents a dataset, a set of managed objectsand management operations, a set of access operations to modify or readthe dataset, and a plurality of storage systems. Such managementoperations may modify or query managed objects equivalently through anyof the storage systems, where access operations to read or modify thedataset operate equivalently through any of the storage systems. Eachstorage system may store a separate copy of the dataset as a propersubset of the datasets stored and advertised for use by the storagesystem, where operations to modify managed objects or the datasetperformed and completed through any one storage system are reflected insubsequent management objects to query the pod or subsequent accessoperations to read the dataset. Additional details regarding a ‘pod’ maybe found in previously filed provisional patent application No.62/518,071, which is incorporated herein by reference.

In some implementations, in response to any one or more storage systemsthat are members of a pod are interrupted, any remaining storagesystems, or any storage systems that resume operation earlier, mayeither detach them (so that they are no longer in-sync) or will wait forthem and participate in a recovery action to ensure consistency beforemoving forward. If the outage is short enough, and recovery is quickenough, then operating systems and applications external to the storagesystems, or running on a storage system that does not fault in a waythat brings the application itself down, may experience a temporarydelay in storage operation processing but may not experience a serviceoutage. SCSI and other storage protocols support retries, including toalternate target storage interfaces, in the case of operations lost dueto a temporary storage controller or interface target controller outage,and SCSI in particular supports a BUSY status which requests initiatorretries which could be used while a storage controller participates inrecovery.

In general, one of the goals of recovery is to handle anyinconsistencies from an unexpected disruption of in-progress,distributed operations and to resolve the inconsistencies by makingin-sync pod member storage systems sufficiently identical. At thatpoint, providing the pod service can be safely resumed. Sufficientlyidentical at least includes the content stored in the pod, and in othercases, sufficiently identical may include the state of persistentreservations. Sufficiently identical may also include ensuring thatsnapshots are either consistent—and still correct with respect tocompleted, concurrent, or more recently received modifying operations—orconsistently deleted. Depending on an implementation, there may be othermetadata that should be made consistent. If there is metadata used fortracking or optimizing the transfer of content from a replication sourceto an asynchronous or snapshot-based replication target, then that mightneed to be made consistent to allow the replication source to switchseamlessly from one member storage system of a pod to another memberstorage system. The existence and properties of volumes may also need tobe recovered, and perhaps definitions related to applications orinitiating host systems. Many of these properties may be recovered usingstandard database transaction recovery techniques, depending on how theyare implemented.

In some examples, beyond ensuring that administrative metadata issufficiently identical in a storage system that implements modifyingoperations to content in a block-based storage system, recovery mustensure that that those modifications are applied or discardedconsistently across a pod and with proper consideration for blockstorage semantics (order, concurrency, consistency, atomicity foroperations such as COMPARE AND WRITE and XDWRITEREAD). Such animplementation is based on being able to know during recovery whatoperations might have been applied to at least one in-sync storagesystem for a pod that might not have been applied to all other in-syncstorage systems for the pod, and either applying them everywhere orbacking them out. Either action results in consistency—apply everywhereor backout everywhere—and there is no inherent reason why the answer hasto be uniform across all operations. Backout may be allowed if at leastone in-sync storage system for the pod did not apply the operation. Ingeneral, it is often simpler to reason about applying all updates thatwere found on any in-sync storage system for a pod rather than backingout some or all updates that are on one or more in-sync storage systemsfor a pod but that are not on all in-sync storage systems for the pod.To be efficient, knowing what was applied on some systems that might nothave been applied on other systems generally requires that the storagesystems record something other than the raw data (otherwise, all datamight have to be compared which could be enormously time consuming).Discussed below is additional detail regarding implementations forrecording such information that may enable storage system recovery.

In some implementations, two examples for persistently trackinginformation for ensuring consistency include: (1) identifying that thecontent of volumes might be different across in-sync storage systems forthe pod, and (2) identifying collections of operations that might nothave been universally applied across all in-sync storage systems for thepod. The first example is a traditional model for mirroring: keep atracking map of logical regions that are being written (often as a listor as a bitmap covering a volume's logical space with some granularity)and use that list during recovery to note which regions might differbetween one copy and another. The tracking map is written to some or allmirrors (or is written separately) prior or during the write of thevolume data in such a way that recovery of the tracking map isguaranteed to cover any volume regions that were in flux at the time ofa fault. Recovery in this first variation generally consists of copyingcontent from one copy to another to make sure they are the same.

The second example in persistent tracking—based on operationtracking—may be useful in storage systems that support synchronouslyreplicating virtual copying of large volume ranges within and betweenvolumes in a pod since this case can be more difficult or expensive totrack simply as potential differences in volume content betweensynchronously replicated storage systems (though see a later sectiondescribing tracking and recovery in content-addressable storagesystems).

Further, in this second example, simple content tracking might work lesswell in storage systems where synchronous replication must track morecomplex information, such as in content tracking graphs with extent andlarger granularity identifiers that drive forms of asynchronousreplication and where the asynchronous replication source can bemigrated or faulted over from one in-sync storage system in a pod toanother. When operations are tracked instead of content, recoveryincludes identifying operations that may not have completed everywhere.Once such operations have been identified, any ordering consistencyissues should be resolved, just as they should be during normal run-timeusing techniques such as leader-defined ordering or predicates orthrough interlock exceptions. An interlock exception is described below,and with regard to predicates, descriptions of relationships betweenoperations and common metadata updates may be described as a set ofinterdependencies between separate, modifying operations—where theseinterdependencies may be described as a set of precursors that oneoperation depends on in some way, where the set of precursors may beconsidered predicates that must be true for an operation to complete.

To continue with this second example, given the identified operations,the operations may then be re-applied. Recorded information aboutoperations should include any metadata changes that should be consistentacross pod member storage systems, and this recorded information canthen be copied and applied. Further, predicates, if they are used todisseminate restrictions on concurrency between leaders and followers,might not need to be preserved, if those predicates drive the order inwhich storage systems persist information, since the persistedinformation implies the various plausible outcomes.

As discussed more thoroughly within U.S. Provisional Patent ApplicationSer. No. 62/470,172 and U.S. Provisional Patent Application Ser. No.62/518,071, references that are incorporated herein in their entirety, aset of in-sync storage systems may implement a symmetric I/O model forproviding data consistency. In a symmetric I/O model, multiple storagesystems may maintain a dataset within a pod, and a member storage systemthat receives an I/O operation may process the I/O operation locallyconcurrent with the processing of the I/O operation on all the otherstorage systems in the pod—where the receiving storage system mayinitiate the processing of the I/O operation on the other storagesystems.

However, in some cases, multiple storage systems may receive independentI/O operations that write to overlapping memory regions. For example, ifa first write comes in to a first storage system, then the first storagesystem may begin persisting the first write locally while also sendingthe first write to a second storage system—while at about the same time,a second write, to an overlapping volume region with the first write, isreceived at a second storage system, where the second storage systembegins persisting the second write locally while also sending the secondwrite to the first storage system. In this scenario, at some point,either the first storage system, the second storage system, or bothstorage systems may notice that there is a concurrent overlap.

Further in this scenario, the first write can not be completed on thefirst storage system until both the second storage system has persistedthe first write and responded with a success indication, and the firststorage system has successfully persisted the first write—where thesecond storage system is in a similar situation with the second write.Because both storage systems have access to both the first and secondwrites, either storage system may detect the concurrent overlap, andwhen one storage system detects the concurrent overlap, the storagesystem may trigger an exception, which is referred to herein as an“interlock exception.” One solution includes the two, or possibly morestorage systems when the scenario is expanded to additional storagesystems, storage systems involved in an interlock exception to reachagreement on which write operation prevails.

In another example, such as in the case of overlapping write requests,write-type requests (e.g., WRITE, WRITE SAME, and UNMAP requests, orcombinations) that were overlapping in time and in volume address rangeat the time of an event that interrupted replication and led to aneventual recovery might have completed inconsistently between thein-sync storage systems. The manner in which this situation is handledcan depend on the implementation of the I/O path during normaloperation. In this example, discussed further below, is a first andsecond write that overlapped in time, where each was received by onestorage system or another for a pod before either was signaled as havingcompleted. This example is readily extended to more than two writes byconsidering each two in turn, and to more than two storage systems byconsidering that a first write and a second write might have completedon more than one storage system, and by considering that a first,second, and third write (or additional writes) might have completedinconsistently on three or more storage systems. The techniquesdescribed are easily extended to these cases.

For example, in a symmetric I/O-based storage system implementationbased on interlock exceptions, only the first write might have completedon one storage system while only the second of the two overlappingwrites might have completed on a second storage system. This case can bedetected by noticing that the ranges overlap between each write, and bynoticing that neither storage system includes the alternate overlappingwrite. If the two writes overlap completely (one completely covers theother), then one of the two writes may simply be copied to the otherstorage system and applied to replace that storage system's content forthat volume address range. If the writes overlap only partially, thenthe content that partially overlaps can be copied from one storagesystem to the other (and applied), while the parts that don't overlapcan be copied between each storage system so that the content is madeuniform and up-to-date on both storage systems.

As another example, in a leader based system with predicates or someother means for the leader to declare that one write precedes another,the storage systems performing the writes may well persist one beforethe other, or persist the two together. In another case, theimplementation may persist the two writes separately and out of order,with the ordering predicates used merely to control completionsignaling. If the implementation allows out-of-order write processing,then the preceding example explains how consistency can be recovered. Incases where storage systems enforce ordering of persistence duringnormal operation, then recovery might still see only the first write ona first storage system, but the first and second writes on a secondstorage system. In that case, the second write can be copied from thesecond storage system to the first storage system as part of recovery.

In another example, snapshots may also be recovered. In some cases, suchas for snapshots concurrent with modifications where a leader determinedsome modifications should be included in the snapshot and othersshouldn't, the recorded information might include information aboutwhether a particular write should be included within a snapshot or not.In that model, it may not be necessary to ensure that everything that aleader decided to include in a snapshot must end up included in thesnapshot after a recovery. If one in-sync storage system for a podrecorded the existence of the snapshot and no in-sync storage system forthe pod recorded a write that was ordered for inclusion in the snapshot,then uniformly applying the snapshot without including that write stillresults in snapshot content that is entirely consistent across allin-sync storage systems for the pod. This discrepancy should only occurin the case of concurrent writes and snapshots that had never beensignaled as completed so no inclusion guarantee is warranted: the leaderassigning predicates and ordering may be necessary only for run-timeconsistency rather than for recovery order consistency.

Further, in cases where recovery identifies a write for inclusion in asnapshot, but where recovery doesn't locate the write, the snapshotoperation itself might safely ignore the snapshot depending on theimplementation. The same argument about snapshots applies to virtualcopying of a volume address range through SCSI EXTENDED COPY and similaroperations: the leader defines which writes to the source address rangemight logically precede the copy and which writes to the target addressrange might logically precede or follow the address range copy. However,during recovery, the same arguments apply as with snapshots: aconcurrent write with a volume range copy could miss either theconcurrent write or the volume range copy as long as the result isconsistent across in-sync storage systems for a pod and does not rollback a modification that had completed everywhere and does not reverse amodification that a dataset consumer might have read.

Further with regard to this example describing recovery of snapshots, ifany storage system applied the write for a COMPARE AND WRITE, then thecomparison must have succeeded on one in-sync storage system for a pod,and run-time consistency should have meant that the comparison shouldhave succeeded on all in-sync storage systems for the pod, so if anysuch storage system had applied the write, it can be copied and appliedto any other in-sync storage system for the pod that had not applied itprior to recovery.

Further still, recovery of XDWRITEREAD or XPWRITE requests (or similararithmetic transformation operations between pre-existing data and newdata) could operate either by delivering the result of thetransformation after reading that result from one storage system, or itcan operate by delivering the operation with the transforming data toother storage systems if it can be ensured that any ordering datapreceding the transforming write is consistent across in-sync storagesystems for the pod and if it can be reliably determined which suchstorage systems had not yet applied the transforming write.

As another example, recovery of metadata may be implemented. In thiscase, recovery should also result in consistent recovery of metadatabetween in-sync storage system for a pod, where that metadata isexpected to be consistent across the pod. As long as this metadata isincluded with operations, these can be applied along with contentupdates described by those operations. The manner in which this data ismerged with existing metadata depends on the metadata and theimplementation. Longer-term change tracking information for drivingasynchronous replication can often be merged quite simply as nearby orotherwise related modifications are identified.

As another example, recording recent activity for operation tracking maybe implemented in various ways to identify operations that were inprogress on in-sync storage systems in a pod at the time of a fault orother type of service interruption that led to a recovery. For example,one model is to record recovery information in modifications to eachin-sync storage system within a pod either atomically with anymodification (which can work well if the updates are staged through fastjournaling devices) or by recording information about operations thatwill be in progress before they can occur. The recorded recoveryinformation may include a logical operation identifier, such as based onthe original request or based on some identifier assigned by a leader aspart of describing the operation, and whatever level of operationdescription may be necessary for recovery to operate.

In this example, information recorded by a storage system for a writethat is to be included in the content of a concurrent snapshot shouldindicate that the write is to be included in the snapshot as well as inthe content of the volume that the write is applied to. In some storagesystem implementations, including cloud-based storage systems andhardware-based storage systems, the content of a snapshot isautomatically included in the content of the volume unless replaced byspecific overlapping content in a newer snapshot or replaced by specificoverlapping content written later to the live the volume. Two concurrentwrite-type requests (e.g., WRITE, WRITE SAME or UNMAP requests, orcombinations) that overlap in time and in volume address may beexplicitly ordered by a leader such that the leader ensures that thefirst write is persisted first to all in-sync storage systems for a podbefore the second one can be persisted by any in-sync storage system forthe pod. This ensures, in a simple way, that inconsistencies cannothappen.

Further, in this example, because concurrent overlapping writes to avolume are very rare, this may be acceptable. In that case, if there isa record on any recovering storage system for the second write, then thefirst write must have completed everywhere so it should not needrecovery. Alternately, a predicate may be described by the leaderrequiring that storage systems order a first write before a secondwrite. The storage systems may then perform both writes together, suchthat they are guaranteed to either both persist or both fail to persist.In another case, the storage system may persist the first write and thenthe second write after the persistence of the first write is assured. ACOMPARE AND WRITE, XDWRITEREAD, or XPWRITE request should be ordered insuch a way that the precursor content is identical on all storagesystems at the time each performs the operation. Alternately, onestorage system might calculate the result and deliver the request to allstorage systems as a regular write-type request. Continuing with thisexample, with regard to making these operations recoverable, trackingwhich operations have completed everywhere may allow their recency to bediscounted and recorded information that causes an operation recoveryanalysis for completed operations can then be either discarded orefficiently skipped over by recovery.

In another example, clearing out completed operations may beimplemented. One example to handle clearing of recorded information isto clear it across all storage systems after the operation is known tohave been processed on all in-sync storage systems for the pod. This canbe implemented by having the storage system which received the requestand which signaled completion send a message to all storage systems forthe pod after completion is signaled, allowing each storage system toclear them out. Recovery then involves querying for all recordedoperations that have not been cleared out across all in-sync storagesystems for the pod that are involved in the recovery. Alternately,these messages could be batched so that they happen periodically (e.g.,every 50 ms), or after some number of operations (say, every 10 to 100).This batching process may reduce message traffic significantly at theexpense of somewhat increased recovery times since more fully completedoperations are reported as potentially incomplete. Further, in a leaderbased implementation (as an example), the leader could be made aware ofwhich operations are completed and it could send out the clear messages.

In another example, a sliding window may be implemented. Such an examplemay work well in implementations based on leaders and followers, wherethe leader may attach a sequence number to operations or collections ofoperations. In this way, in response to the leader determining that alloperations up to some sequence number have completed, it may send amessage to all in-sync storage systems indicating that all operations upto that sequence number have completed. The sequence number could alsobe an arbitrary number, such that when all operations associated with anarbitrary number have completed, a message is sent to indicate all thoseoperations have completed. With a sequence number based model, recoverycould query for all operations on any in-sync storage system associatedwith a sequence number larger than the last completed sequence number.In a symmetric implementation without a leader, each storage system thatreceives request for the pod could define its own sliding window andsliding window identity space. In that case, recovery may includequerying for all operations on any in-sync storage window that areassociated with any sliding window identity space whose sliding windowidentity is after the last identity which has completed where operationsfor all preceding identifiers have also completed.

In another example, checkpoints may be implemented. In a checkpointmodel, special operations may be inserted by a leader which depend onthe completion of a uniform set of precursor operations and that allsuccessive operations then depend on. Each storage system may thenpersist the checkpoint in response to all precursor operations havingbeen persisted or completed. A successive checkpoint may be startedsometime after the previous checkpoint has been signaled as persisted onall in-sync storage systems for the pod. A successive checkpoint wouldthus not be initiated until some time after all precursor operations arepersisted across the pod; otherwise, the previous checkpoint would nothave completed. In this model, recovery may include querying for alloperations on all in in-sync storage systems that follow after theprevious to last checkpoint. This could be accomplished by identifyingthe second to last checkpoint known to any in-sync storage system forthe pod, or by asking each storage system to report all operations sinceits second to last persisted checkpoint. Alternately, recovery mayinclude searching for the last checkpoint known to have completed on allin-sync storage systems and may include querying for all operations thatfollow on any in-sync storage system—if a checkpoint completed on allin-sync storage systems, then all operations prior to that checkpointwere clearly persisted everywhere.

In another example, recovery of pods based on replicated directedacyclic graphs of logical extents may be implemented. However, prior todescribing such an implementation, storage systems using directedacyclic graphs of logical extents are first described.

A storage system may store data in accordance with directed acyclicgraphs comprising logical extents. In such a model, logical extents canbe categorized into two types: leaf logical extents, which referencesome amount of stored data in some way, and composite logical extents,which reference other leaf or composite logical extents.

In this example, a leaf extent can reference data in a variety of ways.It can point directly to a single range of stored data (e.g., 64kilobytes of data), or it can be a collection of references to storeddata (e.g., a 1 megabyte “range” of content that maps some number ofvirtual blocks associated with the range to physically stored blocks).In the latter case, these blocks may be referenced using some identity,and some blocks within the range of the extent may not be mapped toanything. Also, in that latter case, these block references need not beunique, allowing multiple mappings from virtual blocks within somenumber of logical extents within and across some number of volumes tomap to the same physically stored blocks. Instead of stored blockreferences, a logical extent could encode simple patterns: for example,a block which is a string of identical bytes could simply encode thatthe block is a repeated pattern of identical bytes.

A composite logical extent can be a logical range of content with somevirtual size, which comprises a plurality of maps that each map from asubrange of the composite logical extent logical range of content to anunderlying leaf or composite logical extent. Transforming a requestrelated to content for a composite logical extent, then, involves takingthe content range for the request within the context of the compositelogical extent, determining which underlying leaf or composite logicalextents that request maps to, and transforming the request to apply toan appropriate range of content within those underlying leaf orcomposite logical extents.

Volumes, or files or other types of storage objects, can be described ascomposite logical extents. Thus, these presented storage objects (whichin most of our discussion will simply be referred to as volumes) can beorganized using this extent model.

Depending on implementation, leaf or composite logical extents could bereferenced from a plurality of other composite logical extents,effectively allowing inexpensive duplication of larger collections ofcontent within and across volumes. Thus, logical extents can be arrangedessentially within an acyclic graph of references, each ending in leaflogical extents. This can be used to make copies of volumes, to makesnapshots of volumes, or as part of supporting virtual range copieswithin and between volumes as part of EXTENDED COPY or similar types ofoperations.

An implementation may provide each logical extent with an identity whichcan be used to name it. This simplifies referencing, since thereferences within composite logical extents become lists comprisinglogical extent identities and a logical subrange corresponding to eachsuch logical extent identity. Within logical extents, each stored datablock reference may also be based on some identity used to name it.

To support these duplicated uses of extents, we can add a furthercapability: copy-on-write logical extents. When a modifying operationaffects a copy-on-write leaf or composite logical extent the logicalextent is copied, with the copy being a new reference and possiblyhaving a new identity (depending on implementation). The copy retainsall references or identities related to underlying leaf or compositelogical extents, but with whatever modifications result from themodifying operation. For example, a WRITE, WRITE SAME, XDWRITEREAD,XPWRITE, or COMPARE AND WRITE request may store new blocks in thestorage system (or use deduplication techniques to identify existingstored blocks), resulting in modifying the corresponding leaf logicalextents to reference or store identities to a new set of blocks,possibly replacing references and stored identities for a previous setof blocks. Alternately, an UNMAP request may modify a leaf logicalextent to remove one or more block references. In both types of cases, aleaf logical extent is modified. If the leaf logical extent iscopy-on-write, then a new leaf logical extent will be created that isformed by copying unaffected block references from the old extent andthen replacing or removing block references based on the modifyingoperation.

Continuing with this example, a composite logical extent that was usedto locate the leaf logical extent may then be modified to store the newleaf logical extent reference or identity associated with the copied andmodified leaf logical extent as a replacement for the previous leaflogical extent. If that composite logical extent is copy-on-write, thena new composite logical extent is created as a new reference or with anew identity, and any unaffected references or identities to itsunderlying logical extents are copied to that new composite logicalextent, with the previous leaf logical extent reference or identitybeing replaced with the new leaf logical extent reference or identity.

In this example, this process continues further backward from referencedextent to referencing composite extent, based on the search path throughthe acyclic graph used to process the modifying operation, with allcopy-on-write logical extents being copied, modified, and replaced.These copied leaf and composite logical extents can then drop thecharacteristic of being copy on write, so that further modifications donot result in an additional copy. For example, the first time someunderlying logical extent within a copy-on-write “parent” compositeextent is modified, that underlying logical extent may be copied andmodified, with the copy having a new identity which is then written intoa copied and replaced instance of the parent composite logical extent.However, a second time some other underlying logical extent is copiedand modified and with that other underlying logical extent copy's newidentity being written to the parent composite logical extent, theparent can then be modified in place with no further copy and replacenecessary on behalf of references to the parent composite logicalextent.

In some implementations, modifying operations to new regions of a volumeor of a composite logical extent for which there is no current leaflogical extent may create a new leaf logical extent to store the resultsof those modifications. If that new logical extent is to be referencedfrom an existing copy-on-write composite logical extent, then thatexisting copy-on-write composite logical extent will be modified toreference the new logical extent, resulting in another copy, modify, andreplace sequence of operations similar to the sequence for modifying anexisting leaf logical extent.

In some implementations, if a parent composite logical extent cannot begrown large enough (based on implementation) to cover an address rangeassociated that includes new leaf logical extents to create for a newmodifying operation, then the parent composite logical extent may becopied into two or more new composite logical extents which are thenreferenced from a single “grandparent” composite logical extent whichyet again is a new reference or a new identity. If that grandparentlogical extent is itself found through another composite logical extentthat is copy-on-write, then that another composite logical extent willbe copied and modified and replaced in a similar way as described inprevious paragraphs. This copy-on-write model can be used as part ofimplementing snapshots, volume copies, and virtual volume address rangecopies within a storage system implementation based on these directedacyclic graphs of logical extents. To make a snapshot as a read-onlycopy of an otherwise writable volume, a graph of logical extentsassociated with the volume is marked copy-on-write and a reference tothe original composite logical extents are retained by the snapshot.Modifying operations to the volume will then make logical extent copiesas needed, resulting in the volume storing the results of thosemodifying operations and the snapshots retaining the original content.Volume copies are similar, except that both the original volume and thecopied volume can modify content resulting in their own copied logicalextent graphs and subgraphs.

In some implementations, virtual volume address range copies can operateeither by copying block references within and between leaf logicalextents (which does not itself involve using copy-on-write techniquesunless changes to block references modifies copy-on-write leaf logicalextents). Alternately, virtual volume address range copies can duplicatereferences to leaf or composite logical extents, which works well forvolume address range copies of larger address ranges.

Further, this allows graphs to become directed acyclic graphs ofreferences rather than merely reference trees. Copy-on-write techniquesassociated with duplicated logical extent references can be used toensure that modifying operations to the source or target of a virtualaddress range copy will result in the creation of new logical extents tostore those modifications without affecting the target or the sourcethat share the same logical extent immediately after the volume addressrange copy operation.

In some implementations, input/output operations for pods may also beimplemented based on replicating directed acyclic graphs of logicalextents. For example, each storage system within a pod could implementprivate graphs of logical extents, such that the graphs on one storagesystem for a pod have no particular relationship to the graphs on anysecond storage system for the pod. However, there is value insynchronizing the graphs between storage systems in a pod. This can beuseful for resynchronization and for coordinating features such asasynchronous or snapshot based replication to remote storage systems.

Further, it may be useful for reducing some overhead for handling thedistribution of snapshot and copy related processing. In such a model,keeping the content of a pod in sync across all in-sync storage systemsfor a pod is essentially the same as keeping graphs of leaf andcomposite logical extents in sync for all volumes across all in-syncstorage systems for the pod, and ensuring that the content of alllogical extents is in-sync. To be in sync, matching leaf and compositelogical extents should either have the same identity or should havemappable identities. Mapping could involve some set of intermediatemapping tables or could involve some other type of identity translation.In some cases, identities of blocks mapped by leaf logical extents couldalso be kept in sync.

In some implementations, a pod implementation based on a leader andfollowers, with a single leader for each pod, the leader can be incharge of determining any changes to the logical extent graphs. If a newleaf or composite logical extent is to be created, it can be given anidentity. If an existing leaf or composite logical extent is to becopied to form a new logical extent with modifications, the new logicalextent can be described as a copy of a previous logical extent with someset of modifications. If an existing logical extent is to be split, thesplit can be described along with the new resulting identities. If alogical extent is to be referenced as an underlying logical extent fromsome additional composite logical extent, that reference can bedescribed as a change to the composite logical extent to reference thatunderlying logical extent.

In some implementations, modifying operations in a pod thus comprisesdistributing descriptions of modifications to logical extent graphs(where new logical extents are created to extend content or wherelogical extents are copied, modified, and replaced to handlecopy-on-write states related to snapshots, volume copies, and volumeaddress range copies) and distributing descriptions and content formodifications to the content of leaf logical extents.

An additional benefit that comes from using metadata in the form ofdirected acyclic graphs, as described above, is that I/O operations thatmodify stored data in physical storage may be given effect at a userlevel through the modification of metadata corresponding to the storeddata in physical storage—without modifying the stored data in physicalstorage. In the disclosed embodiments of storage systems, where thephysical storage may be a solid state drive, the wear that accompaniesmodifications to flash memory may be avoided or reduced due to I/Ooperations being given effect through the modifications of the metadatarepresenting the data targeted by the I/O operations instead of throughthe reading, erasing, or writing of flash memory.

Further, in some implementations of a cloud-based storage system(1400A), the metadata described above may be used to handle therelationship between virtual, or logical, addresses and physical, orreal, addresses, such as location information within tiers of cloudstorage.

In some implementations, leader storage systems may perform their ownlocal operations to implement these descriptions in the context of theirlocal copy of the pod dataset and the local storage system's metadata.Further, the in-sync followers perform their own separate localoperations to implement these descriptions in the context of theirseparate local copy of the pod dataset and their separate local storagesystem's metadata. When both leader and follower operations arecomplete, the result is compatible graphs of logical extents withcompatible leaf logical extent content. These graphs of logical extentsthen become a type of “common metadata” as described in previousexamples. This common metadata can be described as dependencies betweenmodifying operations and required common metadata. Transformations tographs can be described as separate operations with a queue predicaterelationship with subsequent modifying operations.

Alternately, in some implementations, each modifying operation thatrelies on a particular same graph transformation that has not yet beenknown to complete across the pod can include the parts of any graphtransformation that it relies on. Processing an operation descriptionthat identifies a “new” leaf or composite logical extent that alreadyexists can avoid creating the new logical extent since that part wasalready handled in the processing of some earlier operation, and caninstead implement only the parts of the operation processing that changethe content of leaf or composite logical extents. It is a role of theleader to ensure that transformations are compatible with each other.

For example, some scenarios can start with two writes come that come infor a pod. A first write replaces a composite logical extent A with acopy of formed as composite logical extent B, replaces a leaf logicalextent C with a copy as leaf logical extent D and with modifications tostore the content for the second write, and further writes leaf logicalextent D into composite logical extent B. Meanwhile, a second writeimplies the same copy and replacement of composite logical extent A withcomposite logical extent B but copies and replaces a different leaflogical extent E with a logical extent F which is modified to store thecontent of the second write, and further writes logical extent F intological extent B. In that case, the description for the first write caninclude the replacement of A with B and C with D and the writing of Dinto composite logical extent B and the writing of the content of thefirst write into leaf extend B; and, the description of the second writecan include the replacement of A with B and E with F and the writing ofF into composite logical extent B, along with the content of the secondwrite which will be written to leaf extent F. A leader or any followercan then separately process the first write or the second write in anyorder, and the end result is B copying and replacing A, D copying andreplacing C, F copying replacing E, and D and F being written intocomposite logical extent B. A second copy of A to form B can be avoidedby recognizing that B already exists. In this way, a leader can ensurethat the pod maintains compatible common metadata for a logical extentgraph across in-sync storage systems for a pod.

Given an implementation of storage systems using directed acyclic graphsof logical extents, recovery of pods based on replicated directedacyclic graphs of logical extents may be implemented. Specifically, inthis example, recovery in pods may be based on replicated extent graphsthen involves recovering consistency of these graphs as well asrecovering content of leaf logical extents. In this implementation ofrecovery, operations may include querying for graph transformations thatare not known to have completed on all in-sync storage systems for apod, as well as all leaf logical extent content modifications that arenot known to have completed across all storage systems for the pod. Suchquerying could be based on operations since some coordinated checkpoint,or could simply be operations not known to have completed where eachstorage system keeps a list of operations during normal operation thathave not yet been signaled as completed.

Continuing with this example, graph transformations may bestraightforward: a graph transformation may create new things, copy oldthings to new things, and copy old things into two or more split newthings, or they modify composite extents to modify their references toother extents. Any stored operation description found on any in-syncstorage system that creates or replaces any logical extent can be copiedand performed on any other storage system that does not yet have thatlogical extent. Operations that describe modifications to leaf orcomposite logical extents can apply those modifications to any in-syncstorage system that had not yet applied them, as long as the involvedleaf or composite logical extents have been recovered properly.

Further in this example, recovery of a pod may include the following:

-   -   querying all in-sync storage systems for leaf and composite        logical extent creations and their precursor leaf and composite        logical extents if any that were not known to have completed on        all in-sync storage systems for the pod;    -   querying all in-sync storage systems for modifying operations to        leaf logical extents that were not known to have completed on        all in-sync storage systems for the pod;    -   querying for logical address range copy operations as new        references to pre-existing leaf and composite logical extents;    -   identifying modifications that are not known to have completed        to leaf logical extents and where that leaf logical extent is        the source for a replacement leaf logical extent that also may        need recovery—so that modifications can be completed to that        leaf logical extent to all in-sync storage systems before the        leaf logical extent copy is recovered on any in-sync storage        systems that had not already copied it;    -   completing all leaf and composite logical extent copy        operations;    -   applying all further updates to leaf and composite logical        extents including naming new logical extent references, updating        leaf logical extent content, or removing logical extent        references; and    -   determining that all necessary actions have completed, at which        point further aspects of recovery can proceed.

In another example, as an alternative to using a logical extent graph,storage may be implemented based on a replicated content-addressablestore. In a content-addressable store, for each block of data (forexample, every 512 bytes, 4096 bytes, 8192 bytes or even 16384 bytes) aunique hash value (sometimes also called a fingerprint) is calculated,based on the block content, so that a volume or an extent range of avolume can be described as a list of references to blocks that have aparticular hash value. In a synchronously replicated storage systemimplementation based on references to blocks with the same hash value,replication could involve a first storage system receiving blocks,calculating fingerprints for those blocks, identifying block referencesfor those fingerprints, and delivering changes to one or a plurality ofadditional storage systems as updates to the mapping of volume blocks toreferenced blocks.

In this example, if a block is found to have already been stored by thefirst storage system, that storage system can use its reference to namethe reference in each of the additional storage systems (either becausethe reference uses the same hash value or because an identifier for thereference is either identical or can be mapped readily).

Alternately, in this example, if a block is not found by the firststorage system, then content of the first storage system may bedelivered to other storage systems as part of the operation descriptionalong with the hash value or identity associated with that blockcontent. Further, each in-sync storage system's volume descriptions arethen updated with the new block references. Recovery in such a store maythen include comparing recently updated block references for a volume.If block references differ between different in-sync storage systems fora pod, then one version of each reference can be copied to other storagesystems to make them consistent. If the block reference on one systemdoes not exist, then it be copied from some storage system that doesstore a block for that reference. Virtual copy operations can besupported in such a block or hash reference store by copying thereferences as part of implementing the virtual copy operation.

With regard to a specific implementation for system recovery, theexample method depicted in FIG. 14 includes receiving (1402), by acloud-based storage system (1400A) among a plurality of storage systems(1400A-1400N) synchronously replicating a dataset (1458), a request tomodify the dataset (1458).

Receiving (1402) a request to modify the dataset (1458) may beimplemented as described above with regard to FIGS. 8-13 that describe acloud-based storage system that communicates with a host over a network,where the communication is in accordance with one or more APIsimplemented by a cloud computing environment (1401) or the cloud-basedstorage system (1400A), and where the request may specify an I/Ooperation (1452).

The example method depicted in FIG. 14 also includes generating (1404)recovery information (1454) indicating whether the request to modify thedataset (1458) has been applied on all storage systems in the pluralityof storage systems (1400A-1400N) synchronously replicating the dataset(1458).

Generating (1404) recovery information (1454) indicating whether therequest to modify the dataset (1458) has been applied on all storagesystems in the plurality of storage systems (1400A-1400N) synchronouslyreplicating the dataset (1458) may be implemented using a variety oftechniques described above, including: recovery based on differencetracking; recovery based on operation tracking, including recovery ofoverlapping writes; recovery of snapshots; recovery of metadata, andcommon metadata; recovery based on recording recent activity foroperation tracking, including clearing out completed operations, using asliding window, and using checkpoints; recovery of pods based onreplicated directed acyclic graphs of logical extents; and tracking andrecovery in a replicated content-addressable store. In short, varioustechniques may be used to generate recovery information, where therecovery information indicates on which storage systems among theplurality of storage systems (1400A-1400N) the request to modify thedataset (1458).

The example method depicted in FIG. 14 also includes, responsive to asystem fault, applying (1406) a recovery action in dependence upon therecovery information (1454) indicating whether the request to modify hasbeen applied on all storage systems in the plurality of storage systems(1400A-1400N) synchronously replicating the dataset (1458).

In some implementations, a recovery action may be implemented byapplying the request to modify the dataset (412) on all storage systemsthat did not apply the request to modify the dataset (1458)—where therecovery information (1458) may include tracking information thatindicates which storage systems among the plurality of storage systems(1400A-1400N) did or did not apply one or more requests to modify thesynchronously replicated dataset (1458), including the most recentlyreceived request. However, in other cases, a recovery action may beimplemented by backing out, or undoing, the application of the requestto modify the dataset (1458) on the set of storage systems thatcompleted, or partially completed, application of the request.

Generally, a default recovery action may be to identify each storagesystem that did not successfully complete the request, and to apply therequest, in addition to any other pending requests to modify the dataset(1458). Other implementations of recovery actions are described abovewith reference to descriptions of: recovery based on differencetracking; recovery based on operation tracking, including recovery ofoverlapping writes; recovery of snapshots; recovery of metadata, andcommon metadata; recovery based on recording recent activity foroperation tracking, including clearing out completed operations, using asliding window, and using checkpoints; recovery of pods based onreplicated directed acyclic graphs of logical extents; and tracking andrecovery in a replicated content-addressable store.

Example embodiments are described largely in the context of a fullyfunctional computer system. Readers of skill in the art will recognize,however, that the present disclosure also may be embodied in a computerprogram product disposed upon computer readable storage media for usewith any suitable data processing system. Such computer readable storagemedia may be any storage medium for machine-readable information,including magnetic media, optical media, or other suitable media.Examples of such media include magnetic disks in hard drives ordiskettes, compact disks for optical drives, magnetic tape, and othersas will occur to those of skill in the art. Persons skilled in the artwill immediately recognize that any computer system having suitableprogramming means will be capable of executing the steps of the methodas embodied in a computer program product. Persons skilled in the artwill recognize also that, although some of the example embodimentsdescribed in this specification are oriented to software installed andexecuting on computer hardware, nevertheless, alternative embodimentsimplemented as firmware or as hardware are well within the scope of thepresent disclosure.

Embodiments can include be a system, a method, and/or a computer programproduct. The computer program product may include a computer readablestorage medium (or media) having computer readable program instructionsthereon for causing a processor to carry out aspects of the presentdisclosure.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present disclosure may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present disclosure.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to some embodimentsof the disclosure. It will be understood that each block of theflowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method comprising: receiving, by thecloud-based storage system, a request to modify a dataset that is storedby the cloud-based storage system, wherein the dataset is synchronouslyreplicated among a plurality of storage systems that includes thecloud-based storage system, wherein a request to modify the dataset isacknowledged as being complete when each of the plurality of storagesystems has modified its copy of the dataset; generating recoveryinformation indicating whether the request to modify the dataset hasbeen applied on all storage systems in the plurality of storage systemssynchronously replicating the dataset; and after a system fault,applying a recovery action in dependence upon the recovery informationindicating whether the request to modify the dataset has been applied onall storage systems in the plurality of storage systems synchronouslyreplicating the dataset.
 2. The method of claim 1, wherein thecloud-based storage system includes a plurality of cloud computinginstances that respectively store a portion of the dataset.
 3. Themethod of claim 2, wherein the cloud computing instances provideblock-level data storage.
 4. The method of claim 1, wherein thecloud-based storage system includes a cloud-based object storage thatstores all portions of the dataset.
 5. The method of claim 1, whereinthe plurality of storage systems includes at least one hardware-basedstorage system.
 6. The method of claim 1, wherein the recoveryinformation includes tracking information from one or more of theplurality of storage systems, and wherein the tracking informationindicates progress toward applying the request to modify the dataset onthe plurality of storage systems.
 7. The method of claim 6, wherein thetracking information includes logging information on which storagesystems of the plurality of storage systems have been sent the requestto modify the dataset.
 8. The method of claim 6, wherein the trackinginformation includes logging information on which storage systems of theplurality of storage systems have acknowledged completing the request tomodify the dataset.
 9. The method of claim 1, wherein the recoveryinformation includes confirmation information from one or more other ofthe plurality of storage systems on whether the request is confirmed tohave been processed, and wherein the confirmation information is basedon the cloud-based storage system querying the one or more of the otherof the plurality of storage systems.
 10. The method of claim 1, whereinthe request to modify the dataset is one of a plurality of requests tomodify the dataset, and wherein the recovery information comprises anorder in which the plurality of requests to modify the dataset are to beapplied.
 11. A cloud-based storage system including: one or more storagecontroller applications, each storage controller application executingin a cloud computing instance, wherein the one or more storagecontroller applications are configured to: receive a request to modify adataset that is stored by the cloud-based storage system, wherein thedataset is synchronously replicated among a plurality of storage systemsthat includes the cloud-based storage system, wherein a request tomodify the dataset is acknowledged as being complete when each of theplurality of storage systems has modified its copy of the dataset;generate recovery information indicating whether the request to modifythe dataset has been applied on all storage systems in the plurality ofstorage systems synchronously replicating the dataset; and after asystem fault, apply a recovery action in dependence upon the recoveryinformation indicating whether the request to modify the dataset hasbeen applied on all storage systems in the plurality of storage systemssynchronously replicating the dataset.
 12. The cloud-based storagesystem of claim 11, wherein a first tier of cloud storage of thecloud-based storage system stores a portion of the dataset, wherein thefirst tier includes block storage.
 13. The cloud-based storage system ofclaim 12, wherein a second tier of cloud storage of the cloud-basedstorage system stores all portions of the dataset, wherein the secondtier includes object storage.
 14. The cloud-based storage system ofclaim 11, wherein the first tier of cloud storage includes a pluralityof cloud computing instances with local storage, and each cloudcomputing instance that executes a storage controller application iscommunicatively coupled to each of the cloud computing instances withlocal storage.
 15. The cloud-based storage system of claim 11, whereinthe plurality of storage systems includes at least one hardware-basedstorage system.
 16. The cloud-based storage system of claim 11, whereinthe recovery information includes tracking information from one or moreof the plurality of storage systems, and wherein the trackinginformation indicates progress toward applying the request to modify thedataset on the plurality of storage systems.
 17. The cloud-based storagesystem of claim 16, wherein the tracking information includes logginginformation on which storage systems of the plurality of storage systemshave been sent the request to modify the dataset.
 18. The cloud-basedstorage system of claim 16, wherein the tracking information includeslogging information on which storage systems of the plurality of storagesystems have acknowledged completing the request to modify the dataset.19. The cloud-based storage system of claim 11, wherein the recoveryinformation includes confirmation information from one or more other ofthe plurality of storage systems on whether the request is confirmed tohave been processed, and wherein the confirmation information is basedon the cloud-based storage system querying the one or more of the otherof the plurality of storage systems.
 20. The cloud-based storage systemof claim 11, wherein the request to modify the dataset is one of aplurality of requests to modify the dataset, and wherein the recoveryinformation comprises an order in which the plurality of requests tomodify the dataset are to be applied.